The first attempt fails after 1m32.3s.
The second attempt completes after 12m57.6s.

The relevant error messages seem to be:

$ cros_sdk --replace --bootstrap

...
 Building package sys-libs/glibc sys-devel/binutils sys-devel/llvm sys-kernel/linux-headers sys-devel/gcc on root
Calculating deps...
Deps calculated in 0m8.4s
[ebuild    fU  ] sys-devel/binutils-2.25.51-r67 [2.23.2] USE="cros_host%* hardened%* -mounted_binutils% -next_binutils% -prev_binutils% -profiling%" 
[ebuild  N     ] dev-util/re2c-0.13.6 
[ebuild  N     ] dev-util/ninja-1.7.1  USE="-doc -emacs {-test} -vim-syntax -zsh-completion" 
[ebuild  NS    ] sys-devel/gcc-4.9.2-r163 [4.7.3-r1] USE="cros_host cxx (multilib) nls openmp thumb wrapper_ccache -gcc_repo -gcj -git_gcc -go -graphite -gtk (-hardened) -hardfp -mounted_gcc -multislot -next_gcc -prev_gcc -profiling -tests -upstream_gcc -vanilla -vtable_verify" 
[ebuild     U  ] sys-kernel/linux-headers-4.4-r5 [3.13]
[ebuild     U  ] sys-libs/glibc-2.23-r9 [2.19-r1] USE="rpc%* -audit% -caps%" 
[ebuild  N     ] app-arch/libarchive-3.3.1  USE="acl bzip2 e2fsprogs expat iconv lzma threads xattr zlib -libressl -lz4 -lzo -nettle -static-libs" ABI_X86="(64) -32 (-x32)" 
[ebuild  N     ] dev-libs/libuv-1.10.0  USE="-static-libs" ABI_X86="(64) -32 (-x32)" 
[ebuild  N     ] dev-util/cmake-3.7.2  USE="ncurses -doc -emacs -qt5 -system-jsoncpp {-test}" 
[ebuild  N     ] sys-devel/llvm-5.0_pre300080_p20170707-r2  USE="libffi multitarget ncurses python static-analyzer (-clang) -debug -default-compiler-rt -default-libcxx -doc -gold -libedit -lldb -llvm-next -llvm-tot -ocaml {-test} -xml" ABI_X86="(64) -32 (-x32)" PYTHON_TARGETS="python2_7" VIDEO_CARDS="radeon" 

...

=== Start output for job gcc-4.9.2-r163 (1m33.0s) ===
gcc-4.9.2-r163: >>> Emerging (1 of 1) sys-devel/gcc-4.9.2-r163::chromiumos
gcc-4.9.2-r163:  * Running stacked hooks for pre_pkg_setup
gcc-4.9.2-r163:  *    sysroot_build_bin_dir ...                                                                                            [ ok ]9.2-r163: 

...

gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/xgcc -B/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/ -B/usr/x86_64-pc-linux-gnu/bin/ -B/usr/x86_64-pc-linux-gnu/lib/ -isystem /usr/x86_64-pc-linux-gnu/include -isystem /usr/x86_64-pc-linux-gnu/sys-include    -g -O2 -pipe -m32 -O2 -g -O2 -pipe   -DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-format -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include  -I. -I. -I../../.././gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/. -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../include -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/config/libbid -DENABLE_DECIMAL_BID_FORMAT  -g0 -finhibit-size-directive -fno-inline -fno-exceptions -fno-zero-initialized-in-bss -fno-toplevel-reorder -fno-tree-vectorize -fno-stack-protector  -I. -I. -I../../.././gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/. -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../include -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/config/libbid -DENABLE_DECIMAL_BID_FORMAT -o crtendS.o -MT crtendS.o -MD -MP -MF crtendS.dep  -fno-omit-frame-pointer -fno-asynchronous-unwind-tables -fpic -c /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/crtstuff.c -DCRT_END -DCRTSTUFFS_O
gcc-4.9.2-r163: /usr/bin/install: cannot stat 'vtv_start_preinit.o': No such file or directory

...

gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/xgcc -B/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/ -B/usr/x86_64-pc-linux-gnu/bin/ -B/usr/x86_64-pc-linux-gnu/lib/ -isystem /usr/x86_64-pc-linux-gnu/include -isystem /usr/x86_64-pc-linux-gnu/sys-include    -g -O2 -pipe -m32 -O2  -g -O2 -pipe   -DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-format -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include   -fpic -mlong-double-80 -DUSE_ELF_SYMVER -g -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector   -fpic -mlong-double-80 -DUSE_ELF_SYMVER -I. -I. -I../../.././gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/. -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../gcc -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/../include -I/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/config/libbid -DENABLE_DECIMAL_BID_FORMAT -DHAVE_CC_TLS  -DUSE_TLS -o morestack.o -MT morestack.o -MD -MP -MF morestack.dep -c -xassembler-with-cpp -include morestack.vis /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9/libgcc/config/i386/morestack.S
gcc-4.9.2-r163: /usr/bin/install: cannot stat 'vtv_end_preinit.o': No such file or directory

...

gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/xgcc -B/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/ -B/usr/x86_64-pc-linux-gnu/bin/ -B/usr/x86_64-pc-linux-gnu/lib/ -isystem /usr/x86_64-pc-linux-gnu/include -isystem /usr/x86_64-pc-linux-gnu/sys-include    -O2  -g -O2 -pipe   -DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-format -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include   -fpic -mlong-double-80 -DUSE_ELF_SYMVER -g -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector  -shared -nodefaultlibs -Wl,--soname=libgcc_s.so.1 -Wl,--version-script=libgcc.map -fuse-ld=bfd -o ./libgcc_s.so.1.tmp -g -O2 -pipe -B./ _muldi3_s.o _negdi2_s.o _lshrdi3_s.o _ashldi3_s.o _ashrdi3_s.o _cmpdi2_s.o _ucmpdi2_s.o _clear_cache_s.o _trampoline_s.o __main_s.o _absvsi2_s.o _absvdi2_s.o _addvsi3_s.o _addvdi3_s.o _subvsi3_s.o _subvdi3_s.o _mulvsi3_s.o _mulvdi3_s.o _negvsi2_s.o _negvdi2_s.o _ctors_s.o _ffssi2_s.o _ffsdi2_s.o _clz_s.o _clzsi2_s.o _clzdi2_s.o _ctzsi2_s.o _ctzdi2_s.o _popcount_tab_s.o _popcountsi2_s.o _popcountdi2_s.o _paritysi2_s.o _paritydi2_s.o _powisf2_s.o _powidf2_s.o _powixf2_s.o _mulsc3_s.o _muldc3_s.o _mulxc3_s.o _divsc3_s.o _divdc3_s.o _divxc3_s.o _bswapsi2_s.o _bswapdi2_s.o _clrsbsi2_s.o _clrsbdi2_s.o _fixunssfsi_s.o _fixunsdfsi_s.o _fixunsxfsi_s.o _fixsfdi_s.o _fixdfdi_s.o _fixxfdi_s.o _fixunssfdi_s.o _fixunsdfdi_s.o _fixunsxfdi_s.o _floatdisf_s.o _floatdidf_s.o _floatdixf_s.o _floatundisf_s.o _floatundidf_s.o _floatundixf_s.o _divdi3_s.o _moddi3_s.o _udivdi3_s.o _umoddi3_s.o _udiv_w_sdiv_s.o _udivmoddi4_s.o cpuinfo_s.o sfp-exceptions_s.o addtf3_s.o divtf3_s.o multf3_s.o negtf2_s.o subtf3_s.o unordtf2_s.o fixtfsi_s.o fixunstfsi_s.o floatsitf_s.o floatunsitf_s.o fixtfdi_s.o fixunstfdi_s.o floatditf_s.o floatunditf_s.o fixtfti_s.o fixunstfti_s.o floattitf_s.o floatuntitf_s.o extendsftf2_s.o extenddftf2_s.o extendxftf2_s.o trunctfsf2_s.o trunctfdf2_s.o trunctfxf2_s.o getf2_s.o letf2_s.o eqtf2_s.o _divtc3_s.o _multc3_s.o _powitf2_s.o enable-execute-stack_s.o unwind-dw2_s.o unwind-dw2-fde-dip_s.o unwind-sjlj_s.o unwind-c_s.o emutls_s.o libgcc.a -lc && rm -f ./libgcc_s.so && if [ -f ./libgcc_s.so.1 ]; then mv -f ./libgcc_s.so.1 ./libgcc_s.so.1.backup; else true; fi && mv ./libgcc_s.so.1.tmp ./libgcc_s.so.1 && (echo "/* GNU ld script"; echo "   Use the shared library, but some functions are only in"; echo "   the static library.  */"; echo "GROUP ( libgcc_s.so.1 -lgcc )" ) > ./libgcc_s.so
gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/collect-ld: line 106: /usr/x86_64-pc-linux-gnu/binutils-bin/2.23.2/ld.bfd: No such file or directory
gcc-4.9.2-r163: collect2: error: ld returned 127 exit status
gcc-4.9.2-r163: make[3]: *** [libgcc_s.so] Error 1
gcc-4.9.2-r163: make[3]: *** Waiting for unfinished jobs....
gcc-4.9.2-r163: rm -f libgcc.a

...

gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/xgcc -B/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/ -B/usr/x86_64-pc-linux-gnu/bin/ -B/usr/x86_64-pc-linux-gnu/lib/ -isystem /usr/x86_64-pc-linux-gnu/include -isystem /usr/x86_64-pc-linux-gnu/sys-include    -O2  -g -O2 -pipe   -DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-format -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include   -fpic -mlong-double-80 -DUSE_ELF_SYMVER -g -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector  -shared -nodefaultlibs -Wl,--soname=libgcc_s.so.1 -Wl,--version-script=libgcc.map -fuse-ld=bfd -o 32/libgcc_s.so.1.tmp -g -O2 -pipe -m32 -B./ _muldi3_s.o _negdi2_s.o _lshrdi3_s.o _ashldi3_s.o _ashrdi3_s.o _cmpdi2_s.o _ucmpdi2_s.o _clear_cache_s.o _trampoline_s.o __main_s.o _absvsi2_s.o _absvdi2_s.o _addvsi3_s.o _addvdi3_s.o _subvsi3_s.o _subvdi3_s.o _mulvsi3_s.o _mulvdi3_s.o _negvsi2_s.o _negvdi2_s.o _ctors_s.o _ffssi2_s.o _ffsdi2_s.o _clz_s.o _clzsi2_s.o _clzdi2_s.o _ctzsi2_s.o _ctzdi2_s.o _popcount_tab_s.o _popcountsi2_s.o _popcountdi2_s.o _paritysi2_s.o _paritydi2_s.o _powisf2_s.o _powidf2_s.o _powixf2_s.o _powitf2_s.o _mulsc3_s.o _muldc3_s.o _mulxc3_s.o _multc3_s.o _divsc3_s.o _divdc3_s.o _divxc3_s.o _divtc3_s.o _bswapsi2_s.o _bswapdi2_s.o _clrsbsi2_s.o _clrsbdi2_s.o _fixunssfsi_s.o _fixunsdfsi_s.o _fixunsxfsi_s.o _fixsfdi_s.o _fixdfdi_s.o _fixxfdi_s.o _fixunssfdi_s.o _fixunsdfdi_s.o _fixunsxfdi_s.o _floatdisf_s.o _floatdidf_s.o _floatdixf_s.o _floatundisf_s.o _floatundidf_s.o _floatundixf_s.o _divdi3_s.o _moddi3_s.o _udivdi3_s.o _umoddi3_s.o _udiv_w_sdiv_s.o _udivmoddi4_s.o cpuinfo_s.o tf-signs_s.o sfp-exceptions_s.o addtf3_s.o divtf3_s.o eqtf2_s.o getf2_s.o letf2_s.o multf3_s.o negtf2_s.o subtf3_s.o unordtf2_s.o fixtfsi_s.o fixunstfsi_s.o floatsitf_s.o floatunsitf_s.o fixtfdi_s.o fixunstfdi_s.o floatditf_s.o floatunditf_s.o extendsftf2_s.o extenddftf2_s.o extendxftf2_s.o trunctfsf2_s.o trunctfdf2_s.o trunctfxf2_s.o enable-execute-stack_s.o unwind-dw2_s.o unwind-dw2-fde-dip_s.o unwind-sjlj_s.o unwind-c_s.o emutls_s.o libgcc.a -lc && rm -f 32/libgcc_s.so && if [ -f 32/libgcc_s.so.1 ]; then mv -f 32/libgcc_s.so.1 32/libgcc_s.so.1.backup; else true; fi && mv 32/libgcc_s.so.1.tmp 32/libgcc_s.so.1 && (echo "/* GNU ld script"; echo "   Use the shared library, but some functions are only in"; echo "   the static library.  */"; echo "GROUP ( libgcc_s.so.1 -lgcc )" ) > 32/libgcc_s.so
gcc-4.9.2-r163: /var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/./gcc/collect-ld: line 106: /usr/x86_64-pc-linux-gnu/binutils-bin/2.23.2/ld.bfd: No such file or directory
gcc-4.9.2-r163: collect2: error: ld returned 127 exit status
gcc-4.9.2-r163: make[5]: *** [libgcc_s.so] Error 1
gcc-4.9.2-r163: make[5]: Leaving directory `/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/x86_64-pc-linux-gnu/32/libgcc'
gcc-4.9.2-r163: make[4]: *** [multi-do] Error 1
gcc-4.9.2-r163: make[4]: Leaving directory `/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/x86_64-pc-linux-gnu/libgcc'
gcc-4.9.2-r163: make[3]: *** [all-multi] Error 2
gcc-4.9.2-r163: make[3]: Leaving directory `/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu/x86_64-pc-linux-gnu/libgcc'
gcc-4.9.2-r163: make[2]: *** [all-stage1-target-libgcc] Error 2
gcc-4.9.2-r163: make[2]: Leaving directory `/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu'
gcc-4.9.2-r163: make[1]: *** [stage1-bubble] Error 2
gcc-4.9.2-r163: make[1]: Leaving directory `/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu'
gcc-4.9.2-r163: make: *** [all] Error 2
gcc-4.9.2-r163:  * ERROR: sys-devel/gcc-4.9.2-r163::chromiumos failed (compile phase):
gcc-4.9.2-r163:  *   emake failed
gcc-4.9.2-r163:  * 
gcc-4.9.2-r163:  * If you need support, post the output of `emerge --info '=sys-devel/gcc-4.9.2-r163::chromiumos'`,
gcc-4.9.2-r163:  * the complete build log and the output of `emerge -pqv '=sys-devel/gcc-4.9.2-r163::chromiumos'`.
gcc-4.9.2-r163:  * The complete build log is located at '/var/log/portage/sys-devel:gcc-4.9.2-r163:20170721-102556.log'.
gcc-4.9.2-r163:  * For convenience, a symlink to the build log is located at '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/temp/build.log'.
gcc-4.9.2-r163:  * The ebuild environment file is located at '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/temp/environment'.
gcc-4.9.2-r163:  * Working directory: '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu'
gcc-4.9.2-r163:  * S: '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9'
gcc-4.9.2-r163: >>> Failed to emerge sys-devel/gcc-4.9.2-r163, Log file:
gcc-4.9.2-r163: >>>  '/var/log/portage/sys-devel:gcc-4.9.2-r163:20170721-102556.log'
gcc-4.9.2-r163: 
gcc-4.9.2-r163:  * Messages for package sys-devel/gcc-4.9.2-r163:
gcc-4.9.2-r163: 
gcc-4.9.2-r163:  * ERROR: sys-devel/gcc-4.9.2-r163::chromiumos failed (compile phase):
gcc-4.9.2-r163:  *   emake failed
gcc-4.9.2-r163:  * 
gcc-4.9.2-r163:  * If you need support, post the output of `emerge --info '=sys-devel/gcc-4.9.2-r163::chromiumos'`,
gcc-4.9.2-r163:  * the complete build log and the output of `emerge -pqv '=sys-devel/gcc-4.9.2-r163::chromiumos'`.
gcc-4.9.2-r163:  * The complete build log is located at '/var/log/portage/sys-devel:gcc-4.9.2-r163:20170721-102556.log'.
gcc-4.9.2-r163:  * For convenience, a symlink to the build log is located at '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/temp/build.log'.
gcc-4.9.2-r163:  * The ebuild environment file is located at '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/temp/environment'.
gcc-4.9.2-r163:  * Working directory: '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9-build-x86_64-pc-linux-gnu'
gcc-4.9.2-r163:  * S: '/var/tmp/portage/sys-devel/gcc-4.9.2-r163/work/gcc-4.9.2/gcc-4.9'
=== Complete: job gcc-4.9.2-r163 (1m32.3s) ===