Disable --watchfs on OSX in preparation for enabling it by default.

There's no timeline right now, but it's unusable on OSX and Oracle has no
plans of fixing it.

--
MOS_MIGRATED_REVID=106486015

src/main/java/com/google/devtools/build/lib/skyframe/LocalDiffAwareness.java

@@ -20,6 +20,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
+import com.google.devtools.build.lib.util.OS;
 import com.google.devtools.build.lib.vfs.ModifiedFileSet;
 import com.google.devtools.build.lib.vfs.PathFragment;
 
@@ -76,6 +77,10 @@ public DiffAwareness maybeCreate(com.google.devtools.build.lib.vfs.Path pathEntr
           return null;
         }
       }
+      // Disable the file watcher on OSX due to https://bugs.openjdk.java.net/browse/JDK-7133447
+      if (OS.getCurrent() == OS.DARWIN) {
+        return null;
+      }
 
       WatchService watchService;
       try {