Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

MFC r321332:

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)
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D11680

MFC 302860: Fix aio system call wrappers in librt.

- Update aio_return/waitcomplete wrappers for the ssize_t return type.
- Fix the aio_return() wrapper to fail with EINVAL on a pending job.
This matches the semantics of the in-kernel system call. Also,
aio_return() returns errors via errno, not via the return value.

Approved by: re (gjb)
Sponsored by: Chelsio Communications