Consolidating the notion of a GNU attribute parameter with the attribute argument list.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189711 91177308-0d34-0410-b5e6-96231b3b80d8
Possibly appeasing the build bots from r189711

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189712 91177308-0d34-0410-b5e6-96231b3b80d8