x11-servers/xwayland-devel: update to 21.0.99.1.910
Explicit sync requires https://github.com/freebsd/drm-kmod/issues/278
and currently disabled at build time due to missing <linux/dma-buf.h>
Changes: https://gitlab.freedesktop.org/xorg/xserver/-/compare/052909ab9...337d8d48b