Move logic to check if a class is tagged with objc_suppress_protocol_methods into a helper.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195559 91177308-0d34-0410-b5e6-96231b3b80d8
Remove optional parameter bit from attribute ObjCSuppressProtocol.

This refines some diagnostics and reduces some boilerplate checking logic.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195560 91177308-0d34-0410-b5e6-96231b3b80d8