Update Unix hints to revise groff detection

The existing detection logic was not working on any groff since at least
1.22.3 (November 2014), as could be seen by uncommenting the "$(info
...)" line.  The regex used to match "nroff --version" output was
insufficiently flexible.

Fixes:
$ (cd doc && rm -f Guidebook && PATH=$HOME/groff-1.22.3/usr/bin:/bin make Guidebook) | grep NROFF
NROFFISGROFF=
$ (cd doc && rm -f Guidebook && PATH=$HOME/groff-1.22.4/usr/bin:/bin make Guidebook) | grep NROFF
NROFFISGROFF=
$ (cd doc && rm -f Guidebook && PATH=$HOME/groff-1.23.0/usr/bin:/bin make Guidebook) | grep NROFF
NROFFISGROFF=
$ (cd doc && rm -f Guidebook && PATH=$HOME/groff-HEAD/usr/bin:/bin make Guidebook) | grep NROFF
NROFFISGROFF=

Use a different approach in Make to recording groff detection.  Use
"grep -c" (which is POSIX-conforming) to count the number of matches so
that we can use the contents of the Make macro `NROFFISGROFF` as a sort
of Boolean, which reads more idiomatically (in my opinion).

Further, instead of trying to lexically analyze a matched line in the
output of "nroff --version" and parse components of a version number out
of it, use GNU troff's built-in facility for extracting its minor
version number by storing the output of a tiny *roff document that
reports that datum (and nothing else).

Ignore warnings in category "scale" in any version of groff, because the
`tmac.n` macro package provokes them.

Clarify comments.

sys/unix/hints/include/misc.370

@@ -70,34 +70,38 @@ NROFF = mandoc
 MAN2TXTPRE = -T ascii
 MAN2TXTPOST= | col -b
 else
-#detection of groff
+#
-NROFFISGROFF := $(shell echo `nroff --version | grep "GNU groff version"`)
+# Detect groff.
+NROFFISGROFF := $(shell echo `nroff --version | grep -c 'GNU.*groff.*version'`)
 #$(info NROFFISGROFF=$(NROFFISGROFF))
-ifneq "$(NROFFISGROFF)" ""
+ifneq "$(NROFFISGROFF)" "0"
-# get the version of groff and flag if it is gt or eq to 1.23
+# Gather groff's minor version number (register `.y`).
-GROFFGE123 := $(shell expr `echo $(NROFFISGROFF) | cut -f2 -d.` \>= 23)
+GROFFMINORVERSION := $(shell printf '.tm \\n[.y]\n' | nroff 2>&1)
-# or less than 1.24
+#$(info GROFFMINORVERSION=$(GROFFMINORVERSION))
-GROFFLT124 := $(shell expr `echo $(NROFFISGROFF) | cut -f2 -d.` \< 24)
+# Silence warnings produced by tmac.n, which NetHack does not modify.
-# -Wtab -Wrange are for the sake of tmac.n.
+NROFF_FLAGS := -wall -Wrange -Wscale -Wtab
-NROFF_FLAGS := -wall -Wtab -Wrange
+# groff <= 1.23 also supported an "el" warning category that was buggy.
-ifneq "$(GROFFLT124)" ""
+GROFFLE123 := $(shell expr $(GROFFMINORVERSION) \<= 23)
-NROFF_FLAGS += -Wel -Wscale
+#$(info GROFFLE123=$(GROFFLE123))
-endif
+ifeq "$(GROFFLE123)" "1"
-endif  # NROFFISGROFF
+NROFF_FLAGS += -Wel
+endif  # end groff less than 1.23
+endif  # end NROFFISGROFF
+# $(info NROFF_FLAGS=$(NROFF_FLAGS))
 
 ifneq "$(NROFFISGROFF)" ""   # It's groff
 # add the -Tascii flag used by groff
 MAN2TXTPRE += -Tascii
-ifneq "$(GROFFGE123)" ""   # It's groff 1.23 or greater
-#$(info GROFFGE123=$(GROFFGE123))
 # nroff in groff 1.23 supports the -P option to pass arguments to the
 # output driver.  -cbou are flags to grotty(1).
+GROFFGE123 := $(shell expr $(GROFFMINORVERSION) \>= 23)
+#$(info GROFFGE123=$(GROFFGE123))
+ifeq "$(GROFFGE123)" "1"
 MAN2TXTPRE += -P -cbou
 MAN2TXTPOST=
 else
 MAN2TXTPRE += -c
-# groff less than 1.23
+endif  # end groff less than 1.23
-endif
 endif  # end groff-specific
 endif  # not USE_MANDOC