Apply by doing:
	cd /usr/src/gnu/usr.bin/groff/nroff
	patch -p0 < 006_nroff.patch

And then reinstall nroff.

Index: nroff.sh
===================================================================
RCS file: /cvs/src/gnu/usr.bin/groff/nroff/nroff.sh,v
retrieving revision 1.1.1.1
retrieving revision 1.2
diff -u -r1.1.1.1 -r1.2
--- nroff.sh	1996/09/14 19:01:54	1.1.1.1
+++ nroff.sh	1999/07/26 22:04:13	1.2
@@ -24,7 +24,7 @@
 		echo "$prog: option $1 requires an argument" >&2
 		exit 1
 		;;
-	-i|-[mrno]*)
+	-i|-S|-[mrno]*)
 		opts="$opts $1";
 		;;
 
@@ -58,4 +58,4 @@
 
 # This shell script is intended for use with man, so warnings are
 # probably not wanted.  Also load nroff-style character definitions.
-exec groff -Wall -mtty-char $T $opts ${1+"$@"}
+exec groff -S -Wall -mtty-char $T $opts ${1+"$@"}