This is essential when clang is running in incremental processing mode because
we don't want to reemit the 'tors over and over again.

Patch by Axel Naumann!

Reviewed by Richard Smith and me. (https://reviews.llvm.org/D25605)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@285277 91177308-0d34-0410-b5e6-96231b3b80d8