Tag build swift-DEVELOPMENT-SNAPSHOT-2017-02-17-a
Merge remote-tracking branch 'origin/swift-4.0-branch' into stable

* origin/swift-4.0-branch:
  Merging r293124: ------------------------------------------------------------------------ r293124 | mkuper | 2017-01-25 17:04:11 -0800 (Wed, 25 Jan 2017) | 9 lines
  Merging r295230: ------------------------------------------------------------------------ r295230 | arnolds | 2017-02-15 12:43:43 -0800 (Wed, 15 Feb 2017) | 11 lines
  Merging r295215: ------------------------------------------------------------------------ r295215 | arnolds | 2017-02-15 10:57:06 -0800 (Wed, 15 Feb 2017) | 11 lines
  Merging r295213: ------------------------------------------------------------------------ r295213 | mkuper | 2017-02-15 10:37:26 -0800 (Wed, 15 Feb 2017) | 10 lines
  Add external project LDC to release notes.
  Merging r292271: