Tag build swift-DEVELOPMENT-SNAPSHOT-2017-02-10-a
Merge remote-tracking branch 'origin/swift-4.0-branch' into stable

* origin/swift-4.0-branch:
  Revert "Revert "Modules: Use a PCMCache to manage memory buffers""
  Revert "Revert "[Modules] Fallback to building the module if a timeout occurs""
  Canonicalize the path provided by -fmodules-cache-path.