Provide a better diagnostic and a fixit for a '.' or '->' before the left paren
of a function call.

This fixes PR5898 and means we now have a better diagnostic here than GCC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186208 91177308-0d34-0410-b5e6-96231b3b80d8