MFC r337992, r338125:
POSIX compliance improvements in the pthread(3) functions.

This basically adds makes use of the C99 restrict keyword, and also
adds some 'const's to four threading functions: pthread_mutexattr_gettype(),
pthread_mutexattr_getprioceiling(), pthread_mutexattr_getprotocol(), and
pthread_mutex_getprioceiling. The changes are in accordance to POSIX/SUSv4-2018.

Hinted by: DragonFlyBSD

Relnotes: yes

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Hide the implementation details about multiple threading libraries
from the synopses of pthread*(3) manpages.

Reviewed by: deischen, davidxu

Bring manpage up-to-date with respect to the scheduling priority
range, and mention the SCHED_OTHER scheduling policy.

Submitted by: davidxu
PR: docs/37843
MFC after: 3 days

Remove mentions of libc_r.

Document interfaces that are supported by libthr.

Have a single set of POSIX threads man pages. The LIBRARY section
of each manpage lists libraries that have corresponding interfaces
implemented.

Prodded by: threads
Reviewed by: deischen

The .Fn function. Use .Xr where appropriate.

mdoc(7) police: Use the new .In macro for #include statements.

Spell "FreeBSD" with "F" and "BSD" in uppercase.

Remove whitespace at EOL.

Change my email address in the copyright notices for the sake of consistency
(jasone@canonware.com --> jasone@freebsd.org).

mdoc(7) cleanup:

. use real function names as `.Nm' macro argument in NAME section. It allows
them to appear in apropos(1) or whatis(1) output.

. replace empty lines with `.Pp' macro.

. replace hardcoded standard names with their `.St' macro equivalents.

. sort cross references in SEE ALSO section

Add missing man pages. Fix various compliance bugs, mostly having to do with
error return values. Implement pthread_mutexattr_gettype().

PR: docs/16537, docs/17538