Thanks to John Cummings.

src/cmd/upas/common/makefile

@@ -0,0 +1,18 @@
+CFLAGS=${UNIX} -g -I. -I../libc -I../common -I/usr/include ${SCFLAGS}
+OBJS=mail.o aux.o string.o ${SYSOBJ}
+AR=ar
+.c.o: ; ${CC} -c ${CFLAGS} $*.c
+
+common.a: ${OBJS}
+	${AR} cr common.a ${OBJS}
+	-ranlib common.a
+
+aux.o:		aux.h string.h mail.h
+string.o:	string.h mail.h
+mail.o:		mail.h
+syslog.o:	sys.h
+mail.h:		sys.h
+
+clean:
+	-rm -f *.[oO] core a.out *.a *.sL common.a
+