PR15539: Record "evaluating if/elif condition" flag in the right place

The previous implementation missed the case where the elif condition was
evaluated from the context of an #ifdef that was false causing PR15539.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177345 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed