Merge remote-tracking branch 'origin/swift-3.1-branch' into stable

* origin/swift-3.1-branch:
  Revert "[analyzer] Re-apply r283093 "Add extra notes to ObjCDeallocChecker""
  [analyzer] DeallocChecker: Don't warn about directly-set IBOutlet ivars on macOS
  [analyzer] Fix build error after r283660 - remove constexpr strings.
  [analyzer] Re-apply r283094 "Improve CloneChecker diagnostics"
  [analyzer] Re-apply r283093 "Add extra notes to ObjCDeallocChecker"
  [analyzer] Re-apply r283092, attempt no.4, chunk no.4 (last)
  [analyzer] Re-apply r283092, attempt no.4, chunk no.3, fixup 1.
  [analyzer] Re-apply r283092, attempt no.4, chunk no.3.
  [analyzer] Re-apply r283092, attempt no.4, chunk no.2.
  [analyzer] Re-apply r283092, attempt no.4, a small chunk.