glsl_to_tgsi: add fallthrough comments

All those cases are supposed to hit an assert in ir_binop_bit_or case.

Signed-off-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5133>
1 file changed