Add missing files
Summary: The current code for GNU/Linux is actually completely generic, and can be moved to Gnu, so it can benefit GNU/Hurd and GNU/kFreeBSD
Reviewers: kristina, sammccall, lebedev.ri, MaskRay, arsenm, phosek
Reviewed By: MaskRay, phosek
Subscribers: wdng, ormris, emaste, arichardson, krytarowski, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D73845
Samuel Thibault