Add OPENBSD_PLATFORMS variable (that I missed in the previous commit)

core/c/jbigi/mbuild-all.sh

@@ -47,6 +47,7 @@ LINUX_PLATFORMS="${X86_PLATFORMS} ${MISC_LINUX_PLATFORMS}"
 FREEBSD_PLATFORMS="${X86_PLATFORMS} ${MISC_FREEBSD_PLATFORMS}"
 # As they say, "Of course it runs NetBSD!"
 NETBSD_PLATFORMS="${FREEBSD_PLATFORMS} ${MISC_LINUX_PLATFORMS} ${MISC_NETBSD_PLATFORMS}"
+OPENBSD_PLATFORM="${X86_PLATFORMS}"
 
 # FIXME Is this all?
 DARWIN_PLATFORMS="core2 corei"