PR15132: Replace "address expression must be an lvalue or a function

designator" diagnostic with more correct and more human-friendly "cannot take
address of rvalue of type 'T'".

For the case of & &T::f, provide a custom diagnostic, rather than unhelpfully
saying "cannot take address of rvalue of type '<overloaded function type>'".

For the case of &array_temporary, treat it just like a class temporary
(including allowing it as an extension); the existing diagnostic wording
for the class temporary case works fine.

llvm-svn: 174262