compiler: ensure glsl types are not created without a reference

compiler: ensure glsl types are not created without a reference

We want to detect invalid refcounting so assert we have at least one
use before creating types.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>