Mark output_base and output_user_root to not be backed up by TimeMachine on Darwin.

This is equivalent to what Xcode does with the directories that it generates as part its builds.

fix for https://github.com/bazelbuild/bazel/issues/1514

--
MOS_MIGRATED_REVID=127927131

src/main/cpp/blaze_util_mingw.cc

diff --git a/src/main/cpp/blaze_util_mingw.cc b/src/main/cpp/blaze_util_mingw.cc
index 6b79f60..20d1ea6 100644
--- a/src/main/cpp/blaze_util_mingw.cc
+++ b/src/main/cpp/blaze_util_mingw.cc
@@ -780,4 +780,8 @@
   return result;
 }
 
+// Not supported.
+void ExcludePathFromBackup(const string &path) {
+}
+
 }  // namespace blaze