Add a check for misbehaving -Wcomment from gcc-4.7 and add
-Wno-comment to the compilation flags if so.

Patch by Filipe Cabecinhas, configure regenerated by me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221323 91177308-0d34-0410-b5e6-96231b3b80d8