Is this still happening on head? 
The code has changed and most likely fixed on Mac. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/93d77b18279f72b6f9a4a94fda79c8c54af0948e

commit 93d77b18279f72b6f9a4a94fda79c8c54af0948e
Author: Abhishek Arya <aarya@google.com>
Date: Tue Oct 25 14:52:47 2016

Roll libFuzzer 9aa0bdd..0a3128c

https://chromium.googlesource.com/chromium/llvm-project/llvm/lib/Fuzzer/+log/9aa0bdd..0a3128c

BUG= 658627 
TBR=aizatsky@chromium.org,mmoroz@chromium.org,kcc@chromium.org,ochang@chromium.org

Review URL: https://codereview.chromium.org/2446233002 .

Cr-Commit-Position: refs/heads/master@{#427350}

[modify] https://crrev.com/93d77b18279f72b6f9a4a94fda79c8c54af0948e/DEPS

https://build.chromium.org/p/chromium.fyi/builders/Libfuzzer%20Upload%20Mac%20ASan/builds/11008 has the roll in c#2, still crashing.

[598/8048] CXX obj/third_party/libFuzzer/libfuzzer/FuzzerTracePC.o
FAILED: obj/third_party/libFuzzer/libfuzzer/FuzzerTracePC.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/third_party/libFuzzer/libfuzzer/FuzzerTracePC.o.d -DV8_DEPRECATION_WARNINGS -DENABLE_NOTIFICATIONS -DENABLE_PLUGINS=1 -DENABLE_PDF=1 -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DUSE_BROWSER_SPELLCHECKER=1 -DNO_TCMALLOC -DMEMORY_TOOL_REPLACES_ALLOCATOR -DMEMORY_SANITIZER_INITIAL_SIZE -DADDRESS_SANITIZER -DUSE_EXTERNAL_POPUP_MENU=1 -DENABLE_WEBRTC=1 -DDISABLE_NACL -DENABLE_EXTENSIONS=1 -DENABLE_TASK_MANAGER=1 -DENABLE_THEMES=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_SUPERVISED_USERS=1 -DUSE_PROPRIETARY_CODECS -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DENABLE_MEDIA_ROUTER=1 -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=284979-1 -DCR_XCODE_VERSION=0511 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORE=0 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -I../.. -Igen -fno-strict-aliasing -fstack-protector -fcolor-diagnostics -arch x86_64 -Wall -Werror -Wextra -Wpartial-availability -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-deprecated-register -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-shift-negative-value -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -O1 -gdwarf-2 -fno-standalone-debug -isysroot /b/build/slave/Libfuzzer_Upload_Mac_ASan/build/src/build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -mmacosx-version-min=10.8 -fvisibility=hidden -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib -Xclang -add-plugin -Xclang find-bad-constructs -Wheader-hygiene -Wstring-conversion -gline-tables-only -gcolumn-info -fno-omit-frame-pointer -fsanitize=address -mllvm -asan-globals=0 -fsanitize-blacklist=../../tools/memory/asan/blacklist.txt -fno-threadsafe-statics -fvisibility-inlines-hidden -std=c++11 -stdlib=libc++ -fno-rtti -fno-exceptions -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include -c ../../third_party/libFuzzer/src/FuzzerTracePC.cpp -o obj/third_party/libFuzzer/libfuzzer/FuzzerTracePC.o
../../third_party/libFuzzer/src/FuzzerTracePC.cpp:271:3: error: call to member function 'TORCInsert' is ambiguous
  TORCInsert(ArgXor, Arg1, Arg2);
  ^~~~~~~~~~
../../third_party/libFuzzer/src/FuzzerTracePC.cpp:332:15: note: in instantiation of function template specialization 'fuzzer::TracePC::HandleCmp<unsigned long>' requested here
  fuzzer::TPC.HandleCmp(__builtin_return_address(0), Idx, (uintptr_t)0);
              ^
../../third_party/libFuzzer/src/FuzzerTracePC.h:118:8: note: candidate function
  void TORCInsert(size_t Idx, uint8_t Arg1, uint8_t Arg2) {
       ^
../../third_party/libFuzzer/src/FuzzerTracePC.h:121:8: note: candidate function
  void TORCInsert(size_t Idx, uint16_t Arg1, uint16_t Arg2) {
       ^
../../third_party/libFuzzer/src/FuzzerTracePC.h:124:8: note: candidate function
  void TORCInsert(size_t Idx, uint32_t Arg1, uint32_t Arg2) {
       ^
../../third_party/libFuzzer/src/FuzzerTracePC.h:127:8: note: candidate function
  void TORCInsert(size_t Idx, uint64_t Arg1, uint64_t Arg2) {
       ^
1 error generated.

It's hard to tell what's going on w/o a proper access to Mac (which I don't have)
So, hopefully Mike can take a look. 

Maybe r285262 is the fix

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ae8e3431534922f8cd01307a825638e23aa0cfce

commit ae8e3431534922f8cd01307a825638e23aa0cfce
Author: inferno <inferno@chromium.org>
Date: Thu Oct 27 03:08:10 2016

Roll libFuzzer 0a3128c..2ed967c

https://chromium.googlesource.com/chromium/llvm-project/llvm/lib/Fuzzer/+log/0a3128c..2ed967c

TBR=kcc@chromium.org,ochang@chromium.org
BUG= 658627 

Review-Url: https://codereview.chromium.org/2453593004
Cr-Commit-Position: refs/heads/master@{#427923}

[modify] https://crrev.com/ae8e3431534922f8cd01307a825638e23aa0cfce/DEPS

Can't test fix until c#7 compile failure is fixed on pdfium :(

Phew! Mac is green, thanks a lot Kostya.
https://build.chromium.org/p/chromium.fyi/builders/Libfuzzer%20Upload%20Mac%20ASan/builds/11305