Merge remote-tracking branch 'origin/swift-4.0-branch' into stable
* origin/swift-4.0-branch:
Turn on -Wblock-capture-autoreleasing by default.
[Sema][ObjC] Make sure -Wblock-capture-autoreleasing issues a warning even in the presence of nullability qualifiers.
Fix test case committed in r293106 so that it passes on targets whose pointers are 4-bytes instead of 8-bytes.
Remove the return type from the check string in test case.
[CodeGen] Suppress emission of lifetime markers if a label has been seen in the current lexical scope.
[Sema] Fix bug in handling of designated initializer.
