PR15884: In the 'taking the address of a temporary' extension, materialize the
temporary to an lvalue before taking its address. This removes a weird special
case from the AST representation, and allows the constant expression evaluator
to deal with it without (broken) hacks.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180866 91177308-0d34-0410-b5e6-96231b3b80d8