[CF] Apply missing includes and cleanups.
[CF] Apply missing includes and cleanups.

Here we apply a few cursory cleanups for porting purposes. These changes
are as follows:

  * move a TARGET_OS_CYGWIN block: it was nested under TARGET_OS_MAC,
    which is probably not intended.

  * include sys/socket.h for TARGET_OS_BSD: which should be provided.

  * include netinet/in.h for !TARGET_OS_WIN32: which is required for
    struct sockaddr_in; from memory, this is included transitively on
    Linux, but not elsewhere.

  * use TARGET_OS_BSD instead of TARGET_OS_UNIX: TARGET_OS_UNIX appears
    no longer used; TARGET_OS_BSD is a synonym for __unix__ anyway.

  * disuse pthread_setname_np for TARGET_OS_BSD: this doesn't appear in
    the FreeBSD manuals, it's not available on OpenBSD, so let's just
    disuse it.

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