Started here: https://build.chromium.org/p/chromium.fyi/builders/CrWinAsan/builds/4532

Err  issue 661209  i mean. https://chromium.googlesource.com/chromium/src/+/c9175dab5210cb05151ee27dc3e9bd54439650e2 looks pretty related; not sure why this is no longer building.

IIRC, this broke a week ago. I never had a chance to dig it.
I started to happen just after this CL landed:
  https://reviews.llvm.org/D29463

I can repro the case. I'm looking to this. Stay tuned.

D:\src\chromium\src>ninja -C out\ninja64
ninja: Entering directory `out\ninja64'
[1/1] Regenerating ninja files
[14435/48004] LINK(DLL) blacklist_test_main_dll.dll blacklist_test_main_dll.dll.lib blacklist_test_main_dll.dll.pdb
FAILED: blacklist_test_main_dll.dll blacklist_test_main_dll.dll.lib blacklist_test_main_dll.dll.pdb
C:/python_27_amd64/files/python.exe ../../build/toolchain/win/tool_wrapper.py link-wrapper environment.x64 False link.ex
e /nologo /IMPLIB:./blacklist_test_main_dll.dll.lib /DLL /OUT:./blacklist_test_main_dll.dll /PDB:./blacklist_test_main_d
ll.dll.pdb @./blacklist_test_main_dll.dll.rsp
client.lib(crashpad_client_win.obj) : error LNK2019: unresolved external symbol __asan_unhandled_exception_filter refere
nced in function "long __cdecl crashpad::`anonymous namespace'::UnhandledExceptionHandler(struct _EXCEPTION_POINTERS *)"
 (?UnhandledExceptionHandler@?A@crashpad@@YAJPEAU_EXCEPTION_POINTERS@@@Z)
./blacklist_test_main_dll.dll : fatal error LNK1120: 1 unresolved externals
[14437/48004] LINK(DLL) chrome_elf.dll chrome_elf.dll.lib chrome_elf.dll.pdb
FAILED: chrome_elf.dll chrome_elf.dll.lib chrome_elf.dll.pdb
C:/python_27_amd64/files/python.exe ../../build/toolchain/win/tool_wrapper.py link-wrapper environment.x64 False link.ex
e /nologo /IMPLIB:./chrome_elf.dll.lib /DLL /OUT:./chrome_elf.dll /PDB:./chrome_elf.dll.pdb @./chrome_elf.dll.rsp
client.lib(crashpad_client_win.obj) : error LNK2019: unresolved external symbol __asan_unhandled_exception_filter refere
nced in function "long __cdecl crashpad::`anonymous namespace'::UnhandledExceptionHandler(struct _EXCEPTION_POINTERS *)"
 (?UnhandledExceptionHandler@?A@crashpad@@YAJPEAU_EXCEPTION_POINTERS@@@Z)
./chrome_elf.dll : fatal error LNK1120: 1 unresolved externals
[14452/48004] CXX obj/third_party/boringssl/boringssl_constant_time_test/file_test.obj
ninja: build stopped: subcommand failed.

https://cs.chromium.org/chromium/src/third_party/crashpad/crashpad/client/crashpad_client_win.cc?q=unhandled_exception_filter&dr=CSs&l=119

should be fixed with:
  https://reviews.llvm.org/D30001

Thanks! Sounds like we're lacking some upstream test coverage here.

The immediate problem is fixed (don't know if someone added upstream tests though). The fix unmasked a new problem, filed  bug 693718  for that.