switch libagx to the precompilation pipeline. see the big comment in the
previous commit for why we're doing this.
while doing so, we move some dispatch stuff. there was so much churn from
precompile that this avoids doing the churn twice. that new header will be used
for DGC down the road.
there's also a small vtn/bindgen patch in here to skip bindgen'ing entrypoints,
as that conflicts with the new dispatch macros. this is the sane behaviour, we
just need to do the full precomp switch across the tree at once.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32339>