From https://build.chromium.org/p/chromium.fyi/builders/ClangToTMac/builds/15025

41422/42100] LINK ./unittests
FAILED: unittests 
export DEVELOPER_DIR=/b/c/builder/ClangToTMac/src/build/mac_files/Xcode.app;  TOOL_VERSION=1494365172 ../../build/toolchain/mac/linker_driver.py ../../third_party/llvm-build/Release+Asserts/bin/clang++  -stdlib=libc++ -arch x86_64 -Werror -isysroot ../../build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.9.0 -Wl,-ObjC -Wl,-rpath,@loader_path/. -Wl,-rpath,@loader_path/../../.. -Wl,-pie -o "./unittests" -Wl,-filelist,"./unittests.rsp" ./libv8_for_testing.dylib ./libv8_libbase.dylib ./libv8_libplatform.dylib ./libicui18n.dylib ./libicuuc.dylib 
Undefined symbols for architecture x86_64:
  "v8::internal::GetRandomMmapAddr()", referenced from:
      v8::internal::HeapTest_ASLR_Test::TestBody() in heap-unittest.o
ld: symbol(s) not found for architecture x86_64
clang-6.0: error: linker command failed with exit code 1 (use -v to see invocation)
Traceback (most recent call last):
  File "../../build/toolchain/mac/linker_driver.py", line 229, in <module>
    Main(sys.argv)
  File "../../build/toolchain/mac/linker_driver.py", line 79, in Main
    subprocess.check_call(compiler_driver_args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)


Build #15015 and #15016 failed for other reasons, so:

Last known good:
https://build.chromium.org/p/chromium.fyi/builders/ClangToTMac/builds/15014
First known bad:
https://build.chromium.org/p/chromium.fyi/builders/ClangToTMac/builds/15017