CodeGen: GLValue exprs in template parameters should have reference type

This fixes a corner-case where __uuidof as a template argument would
result in us trying to emit a GLValue as an RValue.  This would lead to
a crash down the road.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220585 91177308-0d34-0410-b5e6-96231b3b80d8