[XCOFF] make .file directive have directory info

The .file directive is changed to only have basename in D36018 for
ELF.

But on AIX, we require the .file directive to also contain the
directory info. This aligns with other AIX compiler like XLC and is
required by some AIX tool like DBX.

Reviewed By: hubert.reinterpretcast

Differential Revision: https://reviews.llvm.org/D99785