cmd/ld: make hostobj work on newer openbsd

Make hostobj work on OpenBSD 5.3/5.4/-current - these have PIE
enabled by default and linking fails since the Go linker generates
objects that are neither PIC nor PIE.

Fixes #5067

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7572049

src/cmd/ld/lib.c

@@ -574,6 +574,8 @@ hostlink(void)
 	}
 	if(HEADTYPE == Hdarwin)
 		argv[argc++] = "-Wl,-no_pie,-pagezero_size,4000000";
+	if(HEADTYPE == Hopenbsd)
+		argv[argc++] = "-Wl,-nopie";
 	
 	if(iself && AssumeGoldLinker)
 		argv[argc++] = "-Wl,--rosegment";