Tag build swift-DEVELOPMENT-SNAPSHOT-2017-01-28-a
Merge remote-tracking branch 'origin/swift-4.0-branch' into stable

* origin/swift-4.0-branch:
  [TLI] Appease spurious MSVC warning using llvm_unreachable. NFC.
  [TLI] Add prototype checking for all remaining LibFuncs.
  [TLI] Alphabetize some of the prototype check switch. NFC.
  [unittests] Alphabetize cmake file list. NFC.