Have audio_device only depend on X11 if use_x11 is set.

BUG=None
NOTRY=True

Review-Url: https://codereview.webrtc.org/2909343002
Cr-Commit-Position: refs/heads/master@{#18335}

webrtc/modules/audio_device/BUILD.gn

@@ -137,10 +137,10 @@ rtc_static_library("audio_device") {
           "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",