Add flags_compatibility script for fuchsia bots.

Change-Id: Ic57f23e16945f83027d9152a70943f43a2282dfd
Bug: b/232740856
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/277222
Reviewed-by: Christoffer Jansson <jansson@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#38277}

tools_webrtc/mb/mb.py

@@ -86,9 +86,7 @@ class WebRTCMetaBuildWrapper(mb.MetaBuildWrapper):
           '--logcat-output-file', '${ISOLATED_OUTDIR}/logcats',
           '--store-tombstones'
       ]
-    elif is_fuchsia:
-      cmdline += ['bin/run_%s' % target]
-    elif is_ios:
+    elif is_ios or is_fuchsia:
       cmdline += [
           vpython_exe, '../../tools_webrtc/flags_compatibility.py',
           'bin/run_%s' % target