Don't hit an assertion failure when calculating the __PRETTY_FUNCTION__

of a member function with parenthesized declarator.

Like this test case:

class Foo {
  const char *(baz)() {
    return __PRETTY_FUNCTION__;
  }
};

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170233 91177308-0d34-0410-b5e6-96231b3b80d8