suppress warnings with recent *roff

This does not fix the actual problem that is causing the warnings.
It merely suppresses the hundreds of warnings until the actual
problem is corrected.

If there is no NROFF_FLAGS defined in a hints file, there should be
no change in behavior.

At this time, only sys/unix/hints/linux.370 sets NROFF_FLAGS.

sys/unix/Makefile.doc

@@ -33,8 +33,8 @@ PSCMD = groff
 # Single page. Might need adjustment to .pl value
 # GUIDECMD= $(GUIDE_PREFORMAT) | perl -pe 's/^(.mt)$$/.pl 4720v\n.in 0\n.po 8\n.ll 64m\n$$1/' | nroff -c -Tascii | $(COLCMD)
 #
-GUIDECMD = $(GUIDE_PREFORMAT) | nroff -c -Tascii | $(COLCMD)
-ONEPAGECMD = $(ONEPAGE_PREFORMAT) | nroff -c -Tascii | $(COLCMD) \
+GUIDECMD = $(GUIDE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
+ONEPAGECMD = $(ONEPAGE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD) \
 	| sed -e '/EOF--EOF/,12345D'
 
 # Only generate output for the current configuration:

sys/unix/hints/linux.370

@@ -336,6 +336,10 @@ CHGRP=true
 VARDIRPERM = 0755
 VARFILEPERM = 0600
 GAMEPERM = 0755
+
+# suppress several hundred warnings with recent *roff
+NROFF_FLAGS = -W font
+
 #
 #-INCLUDE cross-pre.370
 #