Store a pointer to the return value in a static alloca and let the debugger use that

Store a pointer to the return value in a static alloca and let the debugger use that
as the variable address for NRVO variables.

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D63361

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@363952 91177308-0d34-0410-b5e6-96231b3b80d8