sysconf(3): a few more markup fixes

sysconf(3): the _SC constants are .Dv

sysconf(3): NUL is not a defined variable

sysconf(3): POSIX text doesn't capitalize "option".

Fix NUL/NULL confusion.

One of these was reported by Mouse in PR 58058.

Add _SC_AVPHYS_PAGES.
getconf(1) add this and SC_PHYS_PAGES.
libc: Use vm.uvmexp2 over vm.meter is it's twice as fast on my setup.
getconf.3: Tidy up wording for SC_PHYS_PAGES.

Fix _SC_TIMER_MAX listing, bump date

branches: 1.50.2;
Bump date for _SC_THREAD_PRIO_PROTECT.

GSoC 2016 Charles Cui: Implement thread priority protection based on work
by Andy Doran. Also document the get/set pshared thread calls as not
implemented, and add a skeleton implementation that is disabled.
XXX: document _sched_protect(2).

GSoC 2016: Charles Cui: Add timer related macros
_POSIX_CPUTIME
_POSIX_THREAD_CPUTIME
_POSIX_DELAYTIMER_MAX

Bump date for previous.

GSoC 2016: Charles Cui: add SEM_NSEMS_MAX

Add _SC_TIMER_MAX

Bump date for previous.

P1003_1B_SEMAPHORE is no longer optional

Remove trailing whitespace.

Add _SC_PHYS_PAGES

branches: 1.40.2; 1.40.4; 1.40.8;
maxmimum -> maximum

Xref limits(3).

Mark up NULL.

Use .In for header files instead of .Ar Pa and variations.

Bump date for last effective change (2008).

Remove redundant markup as .Bl does vertical spacing already.

branches: 1.34.6; 1.34.8;
Add support for missing _SC_* constants for sysconf().
From andy dot shevchenko at gmail dot com

branches: 1.33.8;
Add _SC_NPROCESSORS_ONLN and _SC_NPROCESSORS_CONF for sysconf(). These
are extensions but are provided by many Unix systems.

branches: 1.32.8;
We support the POSIX Clock Selection Option.

branches: 1.31.6;
Document _SC_GETGR_R_SIZE_MAX and _SC_GETPW_R_SIZE_MAX

s/the the/the/ (only in sources that aren't regularly imported from
elsewhere).

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

Fix pasto in 1.26; spotted by Thomas Klausner.

Drop trailing spaces.

Mention related kernel options where applicable.

Grammar and mdoc fixes from jmc@openbsd.

Use
.In header.h
instead of
.Fd #include \*[Lt]header.h\*[Gt]
Much easier to read and write, and supported by groff for ages.
Okayed by ross.

Drop trailing whitespace.

Add sysconf(3) knobs for recent additions.

Add a sysconf(3) knob for {ATEXIT_MAX}.

Untangle the description of {MONOTONIC_CLOCK} somewhat.

Generate <>& symbolically.

Add {POSIX_MONOTONIC_CLOCK} variables.

Standardize section headers, sort sections, sort SEE ALSO, punctuation
and misc. fixes.

Boring whitespace fixes.

branches: 1.15.2;
{OPEN_MAX} does not apply to a user but a single process; noticed by Brook
Milligan on current-users.

branches: 1.14.6;
Move {XOPEN_SHM} from Commands & Utilities to System Interfaces.

1003.1c: add {LOGIN_NAME_MAX}.

branches: 1.12.2;
Add compile-time and run-time feature test knobs for the 1003.1 Mapped Files,
Process Memory Locking, Range Memory Locking and Memory Protection options.

branches: 1.11.2;
Last of the .Os cleanups. .Os is defined in the tmac.doc-common file,
so we shouldn't override it with versions in the manpages. Wheee!

Add missing .El lines.

Add support for _SC_SYNCHRONIZED_IO and _SC_IOV_MAX. Rearrange documentation
a bit, and actually document _SC_XOPEN_SHM.

Add support to query PAGESIZE, PAGE_SIZE, _POSIX_FSYNC and _XOPEN_SHM via
sysconf().

Fix mdoc .Xr reference for syntax or correctness (e.g. exec(2) versus exec(3)).
Make other mdoc corrections as inspection dictated.

add LIBRARY section to man page

.Bx'ize

Add missing `STANDARDS' compliance statements. As we #define _POSIX_VERSION
to 199009L, bump existing statements to 1003.1-1990.

Manpage fixes from Jochen Pohl. Aligns the prototypes in the SYNOPSIS
section with the actual function declarations. Also fixes decription
of _SC_CLK_TCK in sysconf(3). See PR #1587 and PR #1589 for details.

merge with 4.4-Lite, keeping local changes. clean up Ids

branches: 1.1.1;
Initial revision