Remove $FreeBSD$: one-line .h pattern

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

Fix aio_readv(2), aio_writev(2) with SIGEV_THREAD.

Add missing wrapper code to librt for these new functions so that
SIGEV_THREAD works. Without machinery to convert it to SIGEV_THREAD_ID,
you got EINVAL.

Reviewed by: asomers
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D31618

Implement SIGEV_THREAD notifications for lio_listio(2)

Our man pages have always indicated that this was supported, but in fact the
feature was never implemented for lio_listio(2).

Reviewed by: jhb, kib (earlier version)
MFC after: 20 days
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D11680

Remove some private symbols from librt

Private functions like __aio_read and _aio_read were exposed in
FBSDprivate_1.0 by r169090, even though they've never been used outside of
librt. Also, remove some weak references from r156136 that have never
resolved.

Reviewed by: kib
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D11649

Export the mq_getfd_np() symbol from librt.so, which allows to get
file descriptor for the given posix mqueue. Export the
timer_oshandle_np() symbol to get ktimer id for the given posix timer.

Requested by: Lewis Donzis <lew@perftech.com>
Reviewed by: jilles
Discussed with: kan
Sponsored by: The FreeBSD Foundation
MFC after: 1 week

Unbreak symbol versioning. I have no idea when it was broken, but it's been
at least a few months if not a year or more.