message: Add additional build path to search for clang binary.
diff: @@ -1600,6 +1600,7 @@ class Base(unittest2.TestCase):
  # Begin Swift modifications
  "llvm-build/Ninja-DebugAssert/llvm-macosx-x86_64/bin/clang",
  "llvm-build/Ninja-ReleaseAssert/llvm-macosx-x86_64/bin/clang",
  + "llvm-build/Ninja-RelWithDebInfoAssert/llvm-macosx-x86_64/bin/clang",
  # End Swift modifications
  "llvm-build/Release+Asserts/x86_64/bin/clang",
  "llvm-build/Debug+Asserts/x86_64/bin/clang",
  