fix appengine (#950)

conncheck.go

@@ -6,7 +6,7 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this file,
 // You can obtain one at http://mozilla.org/MPL/2.0/.
 
-// +build !windows
+// +build !windows,!appengine
 
 package mysql
 

conncheck_windows.go → conncheck_dummy.go

@@ -1,5 +1,3 @@
-package mysql
-
 // Go MySQL Driver - A MySQL-Driver for Go's database/sql package
 //
 // Copyright 2019 The Go-MySQL-Driver Authors. All rights reserved.
@@ -8,6 +6,10 @@ package mysql
 // License, v. 2.0. If a copy of the MPL was not distributed with this file,
 // You can obtain one at http://mozilla.org/MPL/2.0/.
 
+// +build windows appengine
+
+package mysql
+
 import "net"
 
 func connCheck(c net.Conn) error {