Better fix for r177725.

It turns out that

-foo;

can be an objective C method declaration. So instead of the previous
solution, recognize objective C methods only if we are in a declaration
scope.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177740 91177308-0d34-0410-b5e6-96231b3b80d8