Add ASAN support for Mac

build/mac/asan.gyp

+# Copyright 2015 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+{
+   'targets': [
+     {
+       'target_name': 'asan_dynamic_runtime',
+       'toolsets': ['target', 'host'],
+       'type': 'none',
+       'variables': {
+         # Every target is going to depend on asan_dynamic_runtime, so allow
+         # this one to depend on itself.
+         'prune_self_dependency': 1,
+         # Path is relative to this GYP file.
+         'asan_rtl_mask_path':
+             '../../third_party/llvm-build/Release+Asserts/lib/clang/*/lib/darwin',
+         'asan_osx_dynamic':
+             '<(asan_rtl_mask_path)/libclang_rt.asan_osx_dynamic.dylib',
+         'asan_iossim_dynamic':
+             '<(asan_rtl_mask_path)/libclang_rt.asan_iossim_dynamic.dylib',
+       },
+       'copies': [
+         {
+           'destination': '<(PRODUCT_DIR)',
+           'files': [
+             '<!(/bin/ls <(asan_osx_dynamic))',
+           ],
+         },
+       ],
+     },
+   ],
+}