some macOS doc updates

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.

sys/unix/Makefile.doc

@@ -83,6 +83,7 @@ $(MAKEDEFS)	: ../util/makedefs.c ../include/config.h ../src/mdlib.c \
 GAME	= nethack
 MANDIR	?= /usr/man/man6
 MANEXT	= 6
+NROFF ?= nroff
 
 # manual installation for most BSD-style systems
 GAMEMANCREATE = cat nethack.6 | $(NHGREP) >
@@ -119,7 +120,7 @@ Guidebook.dat	: Gbk-1pg-pfx.mn Gbk-1pg-sfx.mn $(GUIDEBOOK_MN) tmac.n tmac.nh \
 # MAN2TXTPRE and MAN2TXTPOST are included so that a hints file can alter
 # both of them as required
 MAN2TXTPOST ?= | col -b
-MAN2TXT = $(NHGREP) | nroff -man $(MAN2TXTPRE) $(MAN2TXTPOST)
+MAN2TXT = $(NHGREP) | $(NROFF) -man $(MAN2TXTPRE) $(MAN2TXTPOST)
 # If you aren't using a hints file, you can uncomment the following
 # line if you have groff 1.23 or greater.
 #MAN2TXT = $(NHGREP) | groff -man -Tascii -P -cbou

sys/unix/hints/include/misc.370

@@ -65,6 +65,11 @@ CPLUSPLUS_NEEDED = 1
 endif
 endif
 
+ifdef USE_MANDOC
+NROFF = mandoc
+MAN2TXTPRE=
+MAN2TXTPOST=
+else
 #detection of groff
 NROFFISGROFF := $(shell echo `nroff --version | grep "GNU groff version"`)
 #$(info NROFFISGROFF=$(NROFFISGROFF))
@@ -86,6 +91,7 @@ MAN2TXTPRE += -c
 # groff less than 1.23
 endif
 endif  # end groff-specific
+endif  # not USE_MANDOC
 
 #end of hints/include/misc.370
 #------------------------------------------------------------------------------

sys/unix/hints/macOS.370

@@ -88,6 +88,9 @@ endif   # WANT_WIN_QT
 
 #-INCLUDE misc.370
 
+# manpages directory
+MANDIR=/usr/share/man/man6
+
 ifeq "$(USE_ASAN)" "1"
 CFLAGS +=-fsanitize=address
 LFLAGS +=-fsanitize=address