This package fails to build on an unstable system. Attached relevant logs and emerge --info
Created attachment 717810 [details] emerge_info emerge --info
Created attachment 717813 [details] xorg-server-1.20.11-r1:20210623-040105.log.xz build log (compressed because it exceeds attachment limit, use 'xzless' to read it)
Should be fixed in this PR. https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/699
The fix is merged upstream.
Fixed in 1.20.12.