Fix inconsistency with/without debug information (-g)

This fixes an inconsistency in code generation when compiling with or
without debug information (-g). When debug information is available in
an empty block, the original test would fail, resulting in possibly
different code.

Patch by: Jeroen Dobbelaere

Differential revision: https://reviews.llvm.org/D49467

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339129 91177308-0d34-0410-b5e6-96231b3b80d8