xwayland: unbreak with xorgproto as subproject

$ pkg info -x xorgproto
xorgproto-2022.1

$ git clone https://gitlab.freedesktop.org/xorg/proto/xorgproto.git subprojects/xorgproto
$ meson setup _build
[...]
Run-time dependency xwaylandproto found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency xwaylandproto

Executing subproject xorgproto

xorgproto| Project name: xorgproto
xorgproto| Project version: 2022.2
[...]
$ meson compile -C _build
[..]
../hw/xwayland/xwayland.c:306:10: fatal error: 'X11/extensions/xwaylandproto.h' file not found
#include <X11/extensions/xwaylandproto.h>
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.