USE_X11 is magically set by the toolchain. Let's tie this to
whether X11 extensions is on or not. WEBRTC_USE_X11 is used
in the audio device module so let's be consistent with that.
Bug: b/143587130
Change-Id: I15b1744c9acb534dbdf2119deb2dc5d17aa04184
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161901
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30080}