[Modules] Rebuild modules on umbrella header mismatch

This restores behavior pre-r230064 since after PCMCache work (r298278)
we don't reload PCMs from disk within the same compiler invocation.

Testcases from r230064 are still left around since they still guarantee
the correct behavior we're expecting.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@298464 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 625d61d6c5d39ebcde60a01d8955c8701734dade)
1 file changed