Fix use-after-free and spurious error during module load

FileManager::invalidateCache is not safe to call when there may be
existing references to the file. What module load failure needs is
to refresh so stale stat() info isn't stored.

This may be the last user of invalidateCache; I'll take a look and
remove it if possible in a future commit.

This caused a use-after-free error as well as a spurious error message
that a module was "found in both 'X.pcm' and 'X.pcm'" in some cases.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209138 91177308-0d34-0410-b5e6-96231b3b80d8
This test doesn't need to be XFAILed anywhere; it just needed to be updated to the appropriate diagnostic wording.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209140 91177308-0d34-0410-b5e6-96231b3b80d8