The (dtrace version of) <sys/proc.h> is needed for kthread_t

(same as the amd64 version).   This should fix (one of) the
current i386 build breakages.

external/cddl/osnet/dev/dtrace/i386/dtrace_subr.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: dtrace_subr.c,v 1.9 2018/05/28 21:05:03 chs Exp $	*/
+/*	$NetBSD: dtrace_subr.c,v 1.10 2018/06/04 20:12:45 kre Exp $	*/
 
 /*
  * CDDL HEADER START
@@ -33,6 +33,7 @@
  * Copyright (c) 2011, Joyent, Inc. All rights reserved.
  */
 
+#include <sys/proc.h>
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/types.h>