xerver-xorg will detect and use libxshmfence regardless of the fact its not in DEPENDS and dri3 may be disabled. There is no configure option for it. There is also a floating dependency on libunwind although this does have a configure option.
Patches sent to the list.
Fixed as of oe-core ff2e96cacc116cf362d4c5dc36f1b846672f98e0.