Add a test for an operator access decl.

In Parser::ParseCXXClassMemberDeclaration(), it was possible to change
      isAccessDecl = NextToken().is(tok::kw_operator);
to
      isAccessDecl = false;
and no tests would fail. Now there's coverage for this.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217519 91177308-0d34-0410-b5e6-96231b3b80d8