Reapply an improved version of r180816/180817.

Do not generate VLAs as complex variables any more, as they are now
correctly represented as breg+0 locations in the backend.

(Paired commit with LLVM: r185966)

rdar://problem/13658587

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185967 91177308-0d34-0410-b5e6-96231b3b80d8