GN: Change rtc_source_set targets --> rtc_static_library

webrtc/modules/audio_conference_mixer/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")
 
 config("audio_conference_mixer_config") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
   include_dirs = [
     "include",
     "../include",
   ]
 }
 
-rtc_source_set("audio_conference_mixer") {
+rtc_static_library("audio_conference_mixer") {
   sources = [
     "include/audio_conference_mixer.h",
     "include/audio_conference_mixer_defines.h",
     "source/audio_conference_mixer_impl.cc",
     "source/audio_conference_mixer_impl.h",
     "source/audio_frame_manipulator.cc",
     "source/audio_frame_manipulator.h",
     "source/memory_pool.h",
     "source/memory_pool_posix.h",
     "source/memory_pool_win.h",
     "source/time_scheduler.cc",
     "source/time_scheduler.h",
   ]
 
   public_configs = [ ":audio_conference_mixer_config" ]
 
   if (is_clang) {
     # Suppress warnings from Chrome's Clang plugins.
     # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
     "../../system_wrappers",
     "../audio_processing",
     "../utility",
   ]
 }