Use echo instead of cat to add prologue to builtins.[ch]

Under some circumstances the headers got overwritten.

bin/sh/mkbuiltins

@@ -1,5 +1,5 @@
 #!/bin/sh -
-#	$NetBSD: mkbuiltins,v 1.18 2003/02/02 21:10:45 dsl Exp $
+#	$NetBSD: mkbuiltins,v 1.19 2003/05/15 10:11:01 dsl Exp $
 #
 # Copyright (c) 1991, 1993
 #	The Regents of the University of California.  All rights reserved.
@@ -55,8 +55,7 @@ fi
 
 exec <$builtins 3> ${objdir}/builtins.c 4> ${objdir}/builtins.h
 
-cat <<EOF >&3
-/*
+echo '/*
  * This file was generated by the mkbuiltins program.
  */
 
@@ -64,10 +63,9 @@ cat <<EOF >&3
 #include "builtins.h"
 
 const struct builtincmd builtincmd[] = {
-EOF
+' >&3
 
-cat <<EOF >&4
-/*
+echo '/*
  * This file was generated by the mkbuiltins program.
  */
 
@@ -81,7 +79,7 @@ struct builtincmd {
 extern const struct builtincmd builtincmd[];
 extern const struct builtincmd splbltincmd[];
 
-EOF
+' >&4
 
 specials=