meson: allow building dri driver without window system if osmesa is classic

This was already enabled for gallium based osmesa with gallium drivers
in 9d10581897ef7cfa0f6c392e2048cc04357281b9, so do the same for classic
driver with classic osmesa.

Fixes: cbbd5bb889a2c271a504c379f36a7cb717a85af4
       ("meson: build classic osmesa")
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
1 file changed