The opt_*.h headers must be included before any system header, except

sys/cdefs.h.  In particular, in case of COMPAT_43, param.h includes
sys/types.h, which includes sys/select.h, which includes
sys/_sigset.h.  The _sigset.h customizes the provided definions based
on COMPAT_43, eliminating osigset_t if symbol is not defined.  The
sys/proc.h is included after opt_compat.h and needs osigset_t.

Move opt_compat.h inclusion into the right place.

Sponsored by:	The FreeBSD Foundation

sys/dev/vt/vt_core.c

@@ -33,10 +33,9 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
-#include <sys/param.h>
-
 #include "opt_compat.h"
 
+#include <sys/param.h>
 #include <sys/consio.h>
 #include <sys/eventhandler.h>
 #include <sys/fbio.h>