imports: fix +build tags to exclude syscall deps on appengine

The following tag

// +build linux,!appengine darwin

Translated to (linux AND !appengine) OR (darwin)

Causing issues on darwin when attempting to run dev_appserver.

Change this to always exclude these files from appengine builds.

Change-Id: Ifd63a884747001797d0b0e828f0c9c391bc7c73c
Reviewed-on: https://go-review.googlesource.com/60911
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>
diff --git a/imports/fastwalk_dirent_ino.go b/imports/fastwalk_dirent_ino.go
index ee85bc4..9fc6de0 100644
--- a/imports/fastwalk_dirent_ino.go
+++ b/imports/fastwalk_dirent_ino.go
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,!appengine darwin
+// +build linux darwin
+// +build !appengine
 
 package imports
 
diff --git a/imports/fastwalk_unix.go b/imports/fastwalk_unix.go
index 5854233..db6ee8d 100644
--- a/imports/fastwalk_unix.go
+++ b/imports/fastwalk_unix.go
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,!appengine darwin freebsd openbsd netbsd
+// +build linux darwin freebsd openbsd netbsd
+// +build !appengine
 
 package imports