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Our current weston version is 6.0.91 and it's pretty old.
The latest stable version is 9.0.0.

This patch updates weston and does necessary changes to
third_party/weston/BUILD.gn to make it compilable with GN.

Bug: 1149588
Change-Id: I8dba452cab131052ae3f85486e1f841fc6304847
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632585Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#844595}