bindgen + llvm-19 optimize out some needed const

[okias]

#define DRM_RS_IOCTL(FOO) \
   static const unsigned long DRM_RS_IOCTL_##FOO = DRM_IOCTL_##FOO

DRM_RS_IOCTL(NOUVEAU_EXEC);

becomes nak_bindings.rs.txt

and code fails later with

error[E0425]: cannot find value `DRM_RS_IOCTL_NOUVEAU_EXEC` in this scope

Original bug: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12008