so we can destroy it even if it was constructed with "DelayInitialization = true",
and we didn't end up calling Preprocessor::Initialize.

Fixes crashes in rdar://11558355

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157892 91177308-0d34-0410-b5e6-96231b3b80d8