go/build: put a space between 'generated by make' and package statement

This prevents the message from showing up in godoc.

R=rsc
CC=golang-dev
https://golang.org/cl/5610046

src/pkg/go/build/Makefile

@@ -4,6 +4,7 @@
 
 syslist.go: ../../../Make.inc Makefile
 	echo '// Generated automatically by make.' >$@
+	echo >>$@
 	echo 'package build' >>$@
 	echo >>$@
 	echo 'const goosList = "$(GOOS_LIST)"' >>$@

src/pkg/go/build/syslist.go

-// Copyright 2011 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Generated automatically by make.
 
 package build