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
MFC after: 1 month
Differential Revision: D16722
. 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