Last good:
https://build.chromium.org/p/chromium.fyi/builders/ClangToTMac/builds/13299
Clang: 296513

First bad:
https://build.chromium.org/p/chromium.fyi/builders/ClangToTMac/builds/13300
Clang: 296535


[33357/39692] LINK ./cert_verify_tool
FAILED: cert_verify_tool 
export DEVELOPER_DIR=/b/c/b/ClangToTMac/src/build/mac_files/Xcode.app;  TOOL_VERSION=1486593434 ../../build/toolchain/mac/linker_driver.py ../../third_party/llvm-build/Release+Asserts/bin/clang++  -stdlib=libc++ -arch x86_64 -Werror -isysroot /b/c/b/ClangToTMac/src/build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -mmacosx-version-min=10.9 -Wl,-ObjC -Wl,-rpath,@loader_path/. -Wl,-rpath,@loader_path/../../.. -Wl,-pie -o "./cert_verify_tool" -Wl,-filelist,"./cert_verify_tool.rsp" ./libnet.dylib ./libbase.dylib ./libprotobuf_lite.dylib ./libcrcrypto.dylib ./libboringssl.dylib ./liburl.dylib ./libbase_i18n.dylib ./libicui18n.dylib ./libicuuc.dylib ./libnet_with_v8.dylib -framework AppKit
Undefined symbols for architecture x86_64:
  "_kSecPolicyAppleSSL", referenced from:
      VerifyUsingPathBuilder(CertInput const&, std::__1::vector<CertInput, std::__1::allocator<CertInput> > const&, std::__1::vector<CertInput, std::__1::allocator<CertInput> > const&, base::Time, base::FilePath const&) in verify_using_path_builder.o
ld: symbol(s) not found for architecture x86_64
clang-5.0: 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)
subprocess.CalledProcessError: Command '['../../third_party/llvm-build/Release+Asserts/bin/clang++', '-stdlib=libc++', '-arch', 'x86_64', '-Werror', '-isysroot', '/b/c/b/ClangToTMac/src/build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk', '-mmacosx-version-min=10.9', '-Wl,-ObjC', '-Wl,-rpath,@loader_path/.', '-Wl,-rpath,@loader_path/../../..', '-Wl,-pie', '-o', './cert_verify_tool', '-Wl,-filelist,./cert_verify_tool.rsp', './libnet.dylib', './libbase.dylib', './libprotobuf_lite.dylib', './libcrcrypto.dylib', './libboringssl.dylib', './liburl.dylib', './libbase_i18n.dylib', './libicui18n.dylib', './libicuuc.dylib', './libnet_with_v8.dylib', '-framework', 'AppKit']' returned non-zero exit status 1