Per https://www.chromium.org/developers/testing/addresssanitizer I made a gn file on my Mac with three lines:

is_asan = true
enable_nacl = false  # Necessary until NaCl GN build is more complete.
is_debug = false  # Release build.

I started building and got:

/V/s/c/src (stack)> ninja -C out/releaseasan all -j 500 -l 23 -k 100
ninja: Entering directory `out/releaseasan'
[45086/419/488] CXX obj/buildtools/third_party/libc++/libc++/chrono.o
FAILED: obj/buildtools/third_party/libc++/libc++/chrono.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/buildtools/third_party/libc++/libc++/chrono.o.d -DV8_DEPRECATION_WARNINGS -DNO_TCMALLOC -DMEMORY_TOOL_REPLACES_ALLOCATOR -DMEMORY_SANITIZER_INITIAL_SIZE -DADDRESS_SANITIZER -DDISABLE_NACL -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=\"300839-1\" -DCR_XCODE_VERSION=0821 -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORE=0 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DLIBCXX_BUILDING_LIBCXXABI -I../.. -Igen -fno-strict-aliasing -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -fcolor-diagnostics -arch x86_64 -O2 -fno-omit-frame-pointer -gdwarf-2 -fno-standalone-debug -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.9 -gline-tables-only -gcolumn-info -fno-omit-frame-pointer -fsanitize=address -fno-sanitize-address-use-after-scope -mllvm -asan-globals=0 -fsanitize-blacklist=../../tools/memory/asan/blacklist.txt -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib -Xclang -add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs -Xclang check-auto-raw-pointer -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -fPIC -fstrict-aliasing -pthread -Werror -Wall -Wno-unused-variable -Wpartial-availability -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -Wno-unused-lambda-capture -Wno-user-defined-warnings -fvisibility=default -fvisibility-inlines-hidden -std=c++11 -stdlib=libc++ -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include -std=c++11 -frtti -c ../../buildtools/third_party/libc++/trunk/src/chrono.cpp -o obj/buildtools/third_party/libc++/libc++/chrono.o
../../buildtools/third_party/libc++/trunk/src/chrono.cpp:41:14: error: 'clock_gettime' is only available on macOS 10.12 or newer [-Werror,-Wunguarded-availability]
    if (0 != clock_gettime(CLOCK_REALTIME, &tp))
             ^~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/time.h:177:5: note: 'clock_gettime' has been explicitly marked partial here
int clock_gettime(clockid_t __clock_id, struct timespec *__tp);
    ^
../../buildtools/third_party/libc++/trunk/src/chrono.cpp:41:14: note: enclose 'clock_gettime' in an @available check to silence this warning
    if (0 != clock_gettime(CLOCK_REALTIME, &tp))
             ^~~~~~~~~~~~~
../../buildtools/third_party/libc++/trunk/src/chrono.cpp:78:14: error: 'clock_gettime' is only available on macOS 10.12 or newer [-Werror,-Wunguarded-availability]
    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
             ^~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/time.h:177:5: note: 'clock_gettime' has been explicitly marked partial here
int clock_gettime(clockid_t __clock_id, struct timespec *__tp);
    ^
../../buildtools/third_party/libc++/trunk/src/chrono.cpp:78:14: note: enclose 'clock_gettime' in an @available check to silence this warning
    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
             ^~~~~~~~~~~~~
2 errors generated.