Try to fix non-asserts CodeGenCXX/vararg-non-pod-ms-compat.cpp

There are two GEP's in the function, and it seems the X64 CHECK
was matching the wrong one.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218645 91177308-0d34-0410-b5e6-96231b3b80d8