Add rtc_include_alsa GN variable

webrtc/modules/audio_device/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("../../webrtc.gni")
 
@@ skipping 108 matching lines @@
       ]
       libs = [
         "log",
         "OpenSLES",
       ]
     }
     if (rtc_use_dummy_audio_file_devices) {
       defines += [ "WEBRTC_DUMMY_FILE_DEVICES" ]
     } else {
       if (is_linux) {
-        sources += [
-          "linux/alsasymboltable_linux.cc",
-          "linux/alsasymboltable_linux.h",
-          "linux/audio_device_alsa_linux.cc",
-          "linux/audio_device_alsa_linux.h",
-          "linux/audio_mixer_manager_alsa_linux.cc",
-          "linux/audio_mixer_manager_alsa_linux.h",
-          "linux/latebindingsymboltable_linux.cc",
-          "linux/latebindingsymboltable_linux.h",
-        ]
-        defines += [ "LINUX_ALSA" ]
-        libs = [ "dl" ]
-        if (use_x11) {
-          libs += [ "X11" ]
+        if (rtc_include_alsa) {
+          sources += [
+            "linux/alsasymboltable_linux.cc",
+            "linux/alsasymboltable_linux.h",
+            "linux/audio_device_alsa_linux.cc",
+            "linux/audio_device_alsa_linux.h",
+            "linux/audio_mixer_manager_alsa_linux.cc",
+            "linux/audio_mixer_manager_alsa_linux.h",
+            "linux/latebindingsymboltable_linux.cc",
+            "linux/latebindingsymboltable_linux.h",
+          ]
+          defines += [ "LINUX_ALSA" ]
+          libs = [ "dl" ]
+          if (use_x11) {
+            libs += [ "X11" ]
+          }
         }
         if (rtc_include_pulse_audio) {
           sources += [
             "linux/audio_device_pulse_linux.cc",
             "linux/audio_device_pulse_linux.h",
             "linux/audio_mixer_manager_pulse_linux.cc",
             "linux/audio_mixer_manager_pulse_linux.h",
             "linux/pulseaudiosymboltable_linux.cc",
             "linux/pulseaudiosymboltable_linux.h",
           ]
@@ skipping 202 matching lines @@
       "android/java/src/org/webrtc/voiceengine/WebRtcAudioManager.java",
       "android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java",
       "android/java/src/org/webrtc/voiceengine/WebRtcAudioTrack.java",
       "android/java/src/org/webrtc/voiceengine/WebRtcAudioUtils.java",
     ]
     deps = [
       "//webrtc/base:base_java",
     ]
   }
 }