Implement the restriction that a function with a ref-qualifier cannot

overload a function without a ref-qualifier (C++0x
[over.load]p2). This, apparently, completes the implementation of
rvalue references for *this.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124321 91177308-0d34-0410-b5e6-96231b3b80d8