_NIODataStructures: repair the build on Windows (#2128)
_NIODataStructures: repair the build on Windows (#2128)

Import `ucrt` which is the MSVC C library to match the behaviour of the
other platforms.  This allows building `_NIODataStructures` on Windows.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio