more MAN2TXT follow-up

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.

sys/unix/Makefile.doc

@@ -115,8 +115,11 @@ Guidebook.dat	: Gbk-1pg-pfx.mn Gbk-1pg-sfx.mn $(GUIDEBOOK_MN) tmac.n tmac.nh \
 	$(ONEPAGECMD) > $@
 
 # plain text output
-#MAN2TXT = $(NHGREP) | nroff -man $(MORE_MAN2TXT_FLAGS) - | $(COLCMD)
+# MORE_MAN2TXT_FLAGS is included so that a hints file can alter the options
-MAN2TXT = $(NHGREP) | nroff -man $(MORE_MAN2TXT_FLAGS) -
+MAN2TXT = $(NHGREP) | nroff -man $(MORE_MAN2TXT_FLAGS)
+# If you aren't using a hints file, you can uncomment the following
+# line if you have groff 1.23 or greater.
+#MAN2TXT = $(NHGREP) | nroff -man -Tascii -P -cbou
 nethack.txt	: nethack.6
 	cat nethack.6 | $(MAN2TXT) > nethack.txt
 recover.txt	: recover.6

sys/unix/hints/include/misc.370

@@ -69,20 +69,21 @@ endif
 NROFFISGROFF := $(shell echo `nroff --version | grep "GNU groff version"`)
 #$(info NROFFISGROFF=$(NROFFISGROFF))
 ifneq "$(NROFFISGROFF)" ""
-# --- version check is not currently needed ---
+# get the version of groff and flag if it is gt or eq to 1.23
-# get the version of groff
+GROFFGE123 := $(shell expr `echo $(NROFFISGROFF) | cut -f2 -d.` \>= 23)
-#GROFFGE123 := $(shell expr `echo $(NROFFISGROFF) | cut -f2 -d.` \>= 23)
-#$(info GROFFGE123=$(GROFFGE123))
-#ifeq "$(GROFFGE123)" "1"
-#NROFF_FLAGS = -W font
-#endif
-# ---
 endif  # NROFFISGROFF
 
 ifneq "$(NROFFISGROFF)" ""   # It's groff
-# add the groff-specific plain text flags
+# add the -Tascii flag used by groff
-MORE_MAN2TXT_FLAGS += -Tascii -P -cbou
+MORE_MAN2TXT_FLAGS += -Tascii
+ifneq "$(GROFFGE123)" ""   # It's groff 1.23 or greater
+#$(info GROFFGE123=$(GROFFGE123))
+# add the groff 1.23 specific plain text flag -P
+MORE_MAN2TXT_FLAGS += -P
 endif
+# add more plain text flags used by groff
+MORE_MAN2TXT_FLAGS += -cbou
+endif  # end groff-specific
 
 #end of hints/include/misc.370
 #------------------------------------------------------------------------------