gallivm: handle llvm coroutines for llvm > 15

gallivm: handle llvm coroutines for llvm > 15

LLVM 15 changed the coroutine presplit function attribute in

735e6c40b5e9 [Coroutines] Convert coroutine.presplit to enum attr

This needed to be updated in mesa.

Cc: mesa-stable
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18815>