Use BSD make syntax to configure for OpenBSD

Makefile

@@ -1,12 +1,18 @@
+UNAME != uname
+
 PREFIX ?= /usr/local
-MANDIR ?= ${PREFIX}/share/man
-ETCDIR ?= ${PREFIX}/etc
+MANDIR ?= ${PREFIX}/man
 RUNDIR ?= /var/run
+.if ${UNAME} == OpenBSD
+ETCDIR ?= /etc
+.else
+ETCDIR ?= ${PREFIX}/etc
+.endif
 
 CFLAGS += -std=c99 -Wall -Wextra -Wpedantic
 CFLAGS += -D'ETCDIR="${ETCDIR}"' -D'RUNDIR="${RUNDIR}"'
 
-RC = FreeBSD/catsitd
+RC_SCRIPT = ${UNAME}/catsitd
 
 -include config.mk
 
@@ -35,13 +41,13 @@ tags: *.c *.h
 	sed -e 's|%%PREFIX%%|${PREFIX}|g' $< > $@
 
 clean:
-	rm -f ${BINS} ${OBJS} ${RC} tags
+	rm -f ${BINS} ${OBJS} ${RC_SCRIPT} tags
 
-install: ${BINS} ${RC} ${MAN5} ${MAN8}
+install: ${BINS} ${RC_SCRIPT} ${MAN5} ${MAN8}
 	install -d ${DESTDIR}${PREFIX}/sbin ${DESTDIR}${ETCDIR}/rc.d
 	install -d ${DESTDIR}${MANDIR}/man5 ${DESTDIR}${MANDIR}/man8
 	install ${BINS} ${DESTDIR}${PREFIX}/sbin
-	install ${RC} ${DESTDIR}${ETCDIR}/rc.d
+	install ${RC_SCRIPT} ${DESTDIR}${ETCDIR}/rc.d
 	install -m 644 ${MAN5} ${DESTDIR}${MANDIR}/man5
 	install -m 644 ${MAN8} ${DESTDIR}${MANDIR}/man8
 
@@ -49,4 +55,4 @@ uninstall:
 	rm -f ${BINS:%=${DESTDIR}${PREFIX}/sbin/%}
 	rm -f ${MAN5:%=${DESTDIR}${MANDIR}/man5/%}
 	rm -f ${MAN8:%=${DESTDIR}${MANDIR}/man8/%}
-	rm -f ${DESTDIR}${ETCDIR}/rc.d/catsitd
+	rm -f ${DESTDIR}${ETCDIR}/rc.d/${RC_SCRIPT:T}