Disable PipeWire on Chromecast builds.

For various reasons is_desktop_linux is true on Chromecast builds though
arguably it should not be. This means that the detection logic previously
used is incorrect for Chromecast builds. Since Chromecast needs to
start enabling use_sysroot, this logic needs to explicitly exclude
is_chromecast.

Bug: b/154635846
Change-Id: I6ced6f7e4c78f9d8d7055018e68090883b9e21bd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174620
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31205}
diff --git a/webrtc.gni b/webrtc.gni
index 9750d4d..21fe0ba 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -115,7 +115,7 @@
   # By default it's only enabled on desktop Linux (excludes ChromeOS) and
   # only when using the sysroot as PipeWire is not available in older and
   # supported Ubuntu and Debian distributions.
-  rtc_use_pipewire = is_desktop_linux && use_sysroot
+  rtc_use_pipewire = is_desktop_linux && use_sysroot && !is_chromecast
 
   # Set this to link PipeWire directly instead of using the dlopen.
   rtc_link_pipewire = false