This was accidentally removed in r260506, even though we only support
non-allocatable global register variables. The general (allocatable) case
is explicitly not supported.

Differential Revision: https://reviews.llvm.org/D27473


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@289455 91177308-0d34-0410-b5e6-96231b3b80d8