Have audio_device only depend on X11 if use_x11 is set.

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 119 matching lines @@
           "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",
-          "X11",
-        ]
+        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",
           ]
           defines += [ "LINUX_PULSE" ]
@@ skipping 201 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",
     ]
   }
 }