[libfuzzer] supporting libfuzzer on mac with asan

testing/libfuzzer/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # LibFuzzer is a LLVM tool for coverage-guided fuzz testing.
 # See http://www.chromium.org/developers/testing/libfuzzer
 #
 # To enable libfuzzer, 'use_libfuzzer' GN option should be set to true.
 
 import("//build/config/features.gni")
@@ skipping 19 matching lines @@
       "../../third_party/llvm/lib/Fuzzer/FuzzerTraceState.cpp",
       "../../third_party/llvm/lib/Fuzzer/FuzzerUtil.cpp",
     ]
   } else if (use_drfuzz) {
     sources += [ "drfuzz_main.cc" ]
   } else {
     sources += [ "unittest_main.cc" ]
   }
 }
 
+# A config used by all fuzzer_tests.
+config("fuzzer_test_config") {
+  if (use_libfuzzer && is_mac) {
+    ldflags = [
+      "-Wl,-U,_LLVMFuzzerCustomMutator",
+      "-Wl,-U,_LLVMFuzzerInitialize",
+    ]
+  }
+}
+
 # Noop config used to tag fuzzer tests excluded from clusterfuzz.
 # Libfuzzer build bot uses this to filter out targets while
 # building an archive for clusterfuzz.
 config("no_clusterfuzz") {
 }
 
 # noop to tag seed corpus rules.
 source_set("seed_corpus") {
 }