https://build.chromium.org/p/chromium.android/builders/Android%20Cronet%20ARMv6%20Builder/builds/5007 / https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.android%2FAndroid_Cronet_ARMv6_Builder%2F5007%2F%2B%2Frecipes%2Fsteps%2Fcompile%2F0%2Fstdout , after resolving  issue 732066  :

FAILED: md5sum_bin exe.unstripped/md5sum_bin exe.unstripped/md5sum_bin.map.gz 
python "../../build/toolchain/gcc_link_wrapper.py" --output="./md5sum_bin" --strip="../../third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-strip" --unstripped-file="./exe.unstripped/md5sum_bin" --map-file "./exe.unstripped/md5sum_bin.map.gz" -- ../../third_party/llvm-build/Release+Asserts/bin/clang++ -Wl,--fatal-warnings -Wl,--build-id=sha1 -fPIC -Wl,-z,noexecstack -Wl,-z,now -Wl,-z,relro -Wl,-z,defs -Wl,--as-needed --gcc-toolchain=../../third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64 -fuse-ld=gold -Wl,--icf=all -Wl,--no-undefined -Wl,--exclude-libs=libgcc.a -Wl,--exclude-libs=libc++_static.a -Wl,--exclude-libs=libvpx_assembly_arm.a --target=arm-linux-androideabi -Werror -Wl,--warn-shared-textrel -Wl,-O1 -Wl,--gc-sections -nostdlib -Wl,--warn-shared-textrel --sysroot=../../third_party/android_tools/ndk/platforms/android-16/arch-arm -Bdynamic -Wl,-z,nocopyreloc -pie -Wl,-wrap,calloc -Wl,-wrap,free -Wl,-wrap,malloc -Wl,-wrap,memalign -Wl,-wrap,posix_memalign -Wl,-wrap,pvalloc -Wl,-wrap,realloc -Wl,-wrap,valloc -L../../third_party/android_tools/ndk/sources/cxx-stl/llvm-libc++/libs/armeabi -o "./exe.unstripped/md5sum_bin" -Wl,--start-group @"./md5sum_bin.rsp"  -Wl,--end-group  ../../third_party/android_tools/ndk/platforms/android-16/arch-arm/usr/lib/crtbegin_dynamic.o -lc++_static -lc++abi -landroid_support -lunwind ../../third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/libgcc.a -lc -ldl -lm -llog ../../third_party/android_tools/ndk/platforms/android-16/arch-arm/usr/lib/crtend_android.o
/usr/local/google/buildbot/src/android/ndk-r12-release/ndk/sources/cxx-stl/llvm-libc++abi/libcxxabi/src/cxa_handlers.cpp:112: error: undefined reference to '__atomic_exchange_4'
clang: error: linker command failed with exit code 1 (use -v to see invocation)