std library thread.rs: fix NetBSD code for ILP32 CPUs.

Author: he32

library/std/src/sys/pal/unix/thread.rs

@@ -424,8 +424,8 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
                     if !set.is_null() {
                         let mut count: usize = 0;
                         if libc::pthread_getaffinity_np(libc::pthread_self(), libc::_cpuset_size(set), set) == 0 {
-                            for i in 0..u64::MAX {
-                                match libc::_cpuset_isset(i, set) {
+                            for i in 0..u32::MAX {
+                                match libc::_cpuset_isset(i.into(), set) {
                                     -1 => break,
                                     0 => continue,
                                     _ => count = count + 1,