Tag build swift-DEVELOPMENT-SNAPSHOT-2016-09-21-a
Merge remote-tracking branch 'origin/swift-3.1-branch' into stable

* origin/swift-3.1-branch:
  Update Clang for D20147 ("DebugInfo: New metadata representation for global variables.")
  [codeview] Don't emit vshape info for classes without vfptrs
  [codeview] Pass through vftable shape information