GN: Change rtc_source_set targets --> rtc_static_library

webrtc/modules/rtp_rtcp/BUILD.gn

 # Copyright (c) 2014 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")
 
-rtc_source_set("rtp_rtcp") {
+rtc_static_library("rtp_rtcp") {
   sources = [
     "include/fec_receiver.h",
     "include/receive_statistics.h",
     "include/remote_ntp_time_estimator.h",
     "include/rtp_header_parser.h",
     "include/rtp_payload_registry.h",
     "include/rtp_receiver.h",
     "include/rtp_rtcp.h",
     "include/rtp_rtcp_defines.h",
     "mocks/mock_rtp_rtcp.h",
@@ skipping 173 matching lines @@
       "test/testFec/test_packet_masks_metrics.cc",
     ]
 
     deps = [
       ":rtp_rtcp",
       "//testing/gtest",
       "//webrtc/test:test_support_main",
     ]
   }  # test_packet_masks_metrics
 }