xwayland: Fix build without glamor
When building Xwayland without glamor support enabled using automake,
the build would fail at link time trying to find
/usr/bin/ld: xwayland-glx.o: in function
egl_drawable_wait_x': hw/xwayland/xwayland-glx.c:102: undefined reference toglamor_block_handler'
Make sure we don't try to build
xwayland-glx.c without glamor in the
Note: Meson build is fine because it's already build only with glamor enabled.