glthread: assume all parameters are fixed if marshal_sync is present

glthread: assume all parameters are fixed if marshal_sync is present

We want glthread to ignore variable-sized parameters if the only thing
we want is to pass the pointer parameter as-is, e.g. when a PBO is bound.
Making it conditional on marshal_sync is kinda hacky, but it's the easiest
path towards handling PBOs, which will use marshal_sync to check whether
a PBO is bound.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9029>