Use one byte of p_pad1[] for p_trace_enabled where xxx_syscall_intern()

can save the result of trace_is_enabled() so that it can be efficiently
determined on every system call without having 2 separate syscall functions.
The death of syscall_fancy() looms.

sys/sys/proc.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: proc.h,v 1.257 2007/10/24 14:50:41 ad Exp $	*/
+/*	$NetBSD: proc.h,v 1.258 2007/11/01 21:57:44 dsl Exp $	*/
 
 /*-
  * Copyright (c) 2006, 2007 The NetBSD Foundation, Inc.
@@ -246,7 +246,8 @@ struct proc {
 	int		p_lflag;	/* l: PL_* flags */
 	int		p_stflag;	/* t: PST_* flags */
 	char		p_stat;		/* s: S* process status. */
-	char		p_pad1[3];
+	char		p_trace_enabled; /* Cached by some syscall_intern() */
+	char		p_pad1[2];
 
 	pid_t		p_pid;		/* (: Process identifier. */
 	LIST_ENTRY(proc) p_pglist;	/* l: List of processes in pgrp. */