Use FileEntryRef for PPCallbacks::FileSkipped

This fixes the issue where a filename dependendency was missing if the file that
was skipped was included through a symlink in an earlier run, if the file
manager was reused between runs.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@369998 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed