Don't rely on execute bit.

gnu/usr.bin/groff/Makefile.cfg

@@ -1,5 +1,6 @@
 BINDIR?=	/usr/bin
 SHAREDIR?=	/usr/share
+SHELL=		/bin/sh
 
 # Define `page' to be letter if your PostScript printer uses 8.5x11
 # paper (USA) and define it to be A4, if it uses A4 paper (rest of the
@@ -118,7 +119,7 @@ CFLAGS+=$(DEFINES)
 	-e "s;@TMAC_MDIR@;$(tmacdir)/mm;g" \
 	-e "s;@BROKEN_SPOOLER_FLAGS@;$(BROKEN_SPOOLER_FLAGS);g" \
 	-e "s;@VERSION@;`cat ${.CURDIR}/../VERSION`;g" \
-	-e "s;@MDATE@;`${.CURDIR}/../mdate.sh $<`;g" \
+	-e "s;@MDATE@;`$(SHELL) ${.CURDIR}/../mdate.sh $<`;g" \
 	-e "s;@g@;$(g);g" \
 	-e "s;@G@;`echo $(g) | tr [a-z] [A-Z]`;g" \
 	$< >$@