cgo: do not reset tag generator between files

Clean up an error message and error exit too.
Insert blank line after "DO NOT EDIT" comment
to keep it from being a doc comment.

Fixes #1213.
Fixes #1222.

R=r
CC=golang-dev
https://golang.org/cl/3608042
diff --git a/misc/cgo/stdio/test1.go b/misc/cgo/stdio/test1.go
new file mode 100644
index 0000000..dce2ef8
--- /dev/null
+++ b/misc/cgo/stdio/test1.go
@@ -0,0 +1,29 @@
+// Copyright 2010 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.
+
+// This file contains test cases for cgo.
+
+package stdio
+
+/*
+// issue 1222
+typedef union {
+	long align;
+} xxpthread_mutex_t;
+
+struct ibv_async_event {
+	union {
+		int x;
+	} element;
+};
+
+struct ibv_context {
+	xxpthread_mutex_t mutex;
+};
+*/
+import "C"
+
+type AsyncEvent struct {
+	event C.struct_ibv_async_event
+}