[SE-0112] Teach MachError to store the underlying NSError.
[SE-0112] Teach MachError to store the underlying NSError.

The error code is now specified by MachErrorCode.

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