Follow-ups so PipeWire's remaining modules compile against real relibc:
- struct ip_mreqn (netinet/in.h): index-based multicast join request, used
with IP_ADD_MEMBERSHIP + the SIOCGIFINDEX ifr_ifindex.
- sched_getcpu(): honest ENOSYS/-1 (Redox exposes no per-thread current-CPU
query) rather than a fabricated CPU number.
- ioctl() declared variadic (int, unsigned long, ...) as in POSIX/glibc, so
ioctl(fd, req, long) no longer trips -Werror=int-conversion; cbindgen's
fixed void* prototype is excluded in favor of this ABI-compatible one.
- sys/vfs.h: glibc-style thin wrapper re-exporting sys/statfs.h.
- sched.h: pull in stddef.h + usize_is_size_t so the sched_getaffinity
size_t parameter resolves.
cargo check clean for x86_64-unknown-redox.
