[infra] Roll clang to match the version used by Flutter

tools/buildtools/mac/clang-format

Index: tools/buildtools/mac/clang-format
diff --git a/tools/buildtools/mac/clang-format b/tools/buildtools/mac/clang-format
new file mode 100755
index 0000000000000000000000000000000000000000..39549a91daa194249274a44c3483d42b8cf7d8b9
--- /dev/null
+++ b/tools/buildtools/mac/clang-format
@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+# Copyright 2017 The Dart 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.
+
+"""Forwards to the clang-format for the MacOS toolchain."""
+
+import os
+import subprocess
+import sys
+
+DART_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+TOOLCHAIN = os.path.join(DART_ROOT, 'buildtools', 'toolchain')
+CLANG_FORMAT = os.path.join(TOOLCHAIN, 'clang+llvm-x86_64-darwin', 'bin', 'clang-format')
+
+def main(argv):
+  return subprocess.call([CLANG_FORMAT] + argv[1:])
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))