Makefile: Run postinstall -d /', not postinstall -d //'.

This happens when doing `build.sh install=/'.  The message is less
confusing and it makes postinstall's job simpler for detecting when
it's installing to / rather than somewhere else.

Author: riastradh

Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.337 2023/06/11 10:43:51 lukem Exp $
+#	$NetBSD: Makefile,v 1.338 2023/09/08 12:01:56 riastradh Exp $
 
 #
 # This is the top-level makefile for building NetBSD. For an outline of
@@ -190,23 +190,23 @@ _POSTINSTALL_X11=-x ${X11SRCDIR:Q}
 
 postinstall-check: .PHONY
 	@echo "   === Post installation checks ==="
-	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR}/ check; if [ $$? -gt 1 ]; then exit 1; fi
+	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR:C/^\/$//}/ check; if [ $$? -gt 1 ]; then exit 1; fi
 	@echo "   ================================"
 
 postinstall-fix: .NOTMAIN .PHONY
 	@echo "   === Post installation fixes ==="
-	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR}/ fix
+	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR:C/^\/$//}/ fix
 	@echo "   ==============================="
 
 postinstall-fix-obsolete: .NOTMAIN .PHONY
 	@echo "   === Removing obsolete files ==="
-	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR}/ fix obsolete
+	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR:C/^\/$//}/ fix obsolete
 	@echo "   ==============================="
 
 postinstall-fix-obsolete_stand: .NOTMAIN .PHONY
 	@echo "   === Removing obsolete files ==="
-	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR}/ fix obsolete_stand
-	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR}/ fix obsolete_stand_debug
+	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR:C/^\/$//}/ fix obsolete_stand
+	${_POSTINSTALL_ENV} ${HOST_SH} ${_POSTINSTALL} -s ${.CURDIR} ${_POSTINSTALL_X11} -d ${DESTDIR:C/^\/$//}/ fix obsolete_stand_debug
 	@echo "   ==============================="