[Diffusion] rL244063: Add missing atomic libcall support.

[Dimitry Andric via cfe-commits]

dim added a comment.

Note that http://reviews.llvm.org/rL252920 does not apply to 3.7 cleanly, a few minor modifications are needed.


Users:
  jyknight (Author, Auditor)
  3.7-release (Auditor)
  cfe-commits (Auditor)
  tstellarAMD (Auditor)
  compnerd (Auditor)
  majnemer (Auditor)
  rsmith (Auditor)

http://reviews.llvm.org/rL244063