[Omit Needless Words] Don't remove a first argument label when the parameter has as default argument.
[Omit Needless Words] Don't remove a first argument label when the parameter has as default argument.

Parameters that have default arguments should have argument labels;
don't remove them on import. Fixes rdar://problem/26611977.

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation