Use update.py --print-clang-version in build/mac/asan.gyp

This matches what we do in build/win/asan.gyp and avoids the problem
that the wildcard can match multiple directories, which can happen
when the version changes.

BUG=none
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/1587753002 .

Cr-Original-Commit-Position: refs/heads/master@{#369268}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e5c134116a97f8c6dfc580de2a3ae9d3d74a9dfd

mac/asan.gyp

@@ -13,7 +13,7 @@
          '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',
+             '../../third_party/llvm-build/Release+Asserts/lib/clang/<!(python ../../tools/clang/scripts/update.py --print-clang-version)/lib/darwin',
          'asan_osx_dynamic':
              '<(asan_rtl_mask_path)/libclang_rt.asan_osx_dynamic.dylib',
          'asan_iossim_dynamic':