[analyzer] pr37209: Fix casts of glvalues to references.

Many glvalue expressions aren't of their respective reference type -
they are simply glvalues of their value type.

This was causing problems when we were trying to obtain type of the original
expression while evaluating certain glvalue bit-casts.

Fixed by artificially forging a reference type to provide to the casting
procedure.

Differential Revision: https://reviews.llvm.org/D46224

llvm-svn: 331558