Allow 'make USE_MANDOC=1 distrib' to be used for generating
the doc/*.txt files for systems that have mandoc and may not have groff.
(macOS Ventura doesn't include groff in the OS).
USE_MANDOC=1 is not restricted only to macOS.
Have hints/macOS.370 specify the /usr/share/man/man6 directory for the macOS
man pages, so that 'make manpages' will target the correct directory on
that platform.
Some changes to achieve the following MAN2TXT commands...
If groff version is 1.23 or greater:
nroff -man -Tascii -P -cbou
If groff version is less than 1.23:
nroff -man -Tascii -c | col -b
If non-groff nroff:
nroff -man | col -b
Closes#1153 again.
Following a commit for Issue #1153, g-branden-robinson commented:
> Mac OS X stayed on _groff_ 1.19.2 for over a decade (presumably due to
> _groff_ 1.20 adopting to GNU GPLv3), until finally dropping _groff_
> altogether for macOS Ventura (2022).
>
> There _has_ been an interface change in that time. The [`-P` option I
> advised about is new to _groff_ 1.23.0 (July 2023)]
> (https://git.savannah.gnu.org/cgit/groff.git/tree/NEWS?h=1.23.0#n86).
> [...]
>
> There is a significant number of _groff_ users via Homebrew (enough that
> we hear from them occasionally via bug reports). Some of these have
> upgraded to 1.23.0 via that mechanism.
> [...]
>
> `nroff -` is not necessary with any _nroff_ known to me; like many other
> Bell Labs Unix programs, it reads from the standard input stream by default
> if not given any operands.
Action taken:
1. Remove the unnecessary ' -' from the nroff command in Makefile.doc.
2. In the misc.370 file containing make snippets to include, test whether
groff >= 1.23, and only insert the -P option for 1.23 or greater.
rename hints/include/multiw-3.370 to hints/include/misc.370
keep the portable nroff options in sys/unix/Makefile.doc,
and relocate the non-portable bits to a variable defined
in sys/unix/hints/include/misc.370
This assumes that the groff options are compatible between
Linux and macOS implementations of groff.
If that turns out not to be the case, this bit:
ifneq "$(NROFFISGROFF)" "" # It's groff
# add the groff-specific plain text flags
MORE_MAN2TXT_FLAGS += -Tascii -P -cbou
endif
should relocate from sys/unix/hints/include/misc.370
to sys/unix/hints/linux.370 and sys/unix/hints/macOS.370,
immediately following the inclusion of misc.370, and the
appropriate platform-specific groff options can be
adjused in whichever of those appropriately needs it.
Closes#1153
