Fix -fno-gnu-inline-asm doesn't catch file scope asm

Summary:
FileScopeAsm should be treated the same as funcion level inline asm.
-fno-gnu-inline-asm should trigger an error if file scope asm is used.
I missed this case from r226340. This should not affect ms-extension
because it is not allowed in the file scope.

Reviewers: bob.wilson, rnk

Reviewed By: rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D9328

llvm-svn: 236044