build: Prevent duplicate inclusion of Makefile.rules, which causes make to warn
like crazy.
 - How no one else is bothered by this I can't understand!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124873 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed