<rdar://problem/13509689> Introduce -module-file-info option that provides informatio...

<rdar://problem/13509689> Introduce -module-file-info option that provides information about a particular module file.

This option can be useful for end users who want to know why they
ended up with a ton of different variants of the "std" module in their
module cache. This problem should go away over time, as we reduce the
need for module variants, but it will never go away entirely.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178148 91177308-0d34-0410-b5e6-96231b3b80d8