GN: Change rtc_source_set targets --> rtc_static_library

webrtc/libjingle/xmpp/BUILD.gn

 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../../build/webrtc.gni")
 
@@ skipping 12 matching lines @@
   }
 }
 
 config("xmpp_inherited_config") {
   defines = [
     "FEATURE_ENABLE_SSL",
     "FEATURE_ENABLE_VOICEMAIL",
   ]
 }
 
-rtc_source_set("rtc_xmpp") {
+rtc_static_library("rtc_xmpp") {
   cflags = []
   sources = [
     "asyncsocket.h",
     "constants.cc",
     "constants.h",
     "jid.cc",
     "jid.h",
     "plainsaslhandler.h",
     "prexmppauth.h",
     "saslcookiemechanism.h",
@@ skipping 102 matching lines @@
     }
   }
 
   if (is_posix && is_debug) {
     # The Chromium build/common.gypi defines this for all posix
     # _except_ for ios & mac.  We want it there as well, e.g.
     # because ASSERT and friends trigger off of it.
     defines += [ "_DEBUG" ]
   }
 }