Revert "Rollup merge of #120589 - devnexen:cpuaff_fbsd_upd, r=clarfonthey"

This reverts commit 0a4206a71433bcad48d9447b080a874b1b06d54f, reversing
changes made to 8f3a9a10173f6c52a20bb31e96ae903360733aaf.

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

diff --git a/library/std/src/sys/thread/unix.rs b/library/std/src/sys/thread/unix.rs
index 11fe569..b7908de 100644
--- a/library/std/src/sys/thread/unix.rs
+++ b/library/std/src/sys/thread/unix.rs
@@ -162,7 +162,6 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
             target_os = "hurd",
             target_os = "linux",
             target_os = "aix",
-            target_os = "freebsd",
             target_vendor = "apple",
             target_os = "cygwin",
             target_os = "redox",
@@ -175,17 +174,9 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
             #[cfg(any(target_os = "android", target_os = "linux"))]
             {
                 quota = cgroups::quota().max(1);
-            }
-
-            #[cfg(any(target_os = "android", target_os = "linux", target_os = "freebsd"))]
-            {
-                #[cfg(not(target_os = "freebsd"))]
-                type Cpuset = libc::cpu_set_t;
-                #[cfg(target_os = "freebsd")]
-                type Cpuset = libc::cpuset_t;
-                let mut set: Cpuset = unsafe { mem::zeroed() };
+                let mut set: libc::cpu_set_t = unsafe { mem::zeroed() };
                 unsafe {
-                    if libc::sched_getaffinity(0, size_of::<Cpuset>(), &mut set) == 0 {
+                    if libc::sched_getaffinity(0, size_of::<libc::cpu_set_t>(), &mut set) == 0 {
                         let count = libc::CPU_COUNT(&set) as usize;
                         let count = count.min(quota);
 
@@ -210,9 +201,34 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
                 }
             }
         }
-        any(target_os = "dragonfly", target_os = "openbsd", target_os = "netbsd") => {
+        any(
+            target_os = "freebsd",
+            target_os = "dragonfly",
+            target_os = "openbsd",
+            target_os = "netbsd",
+        ) => {
             use crate::ptr;
 
+            #[cfg(target_os = "freebsd")]
+            {
+                let mut set: libc::cpuset_t = unsafe { mem::zeroed() };
+                unsafe {
+                    if libc::cpuset_getaffinity(
+                        libc::CPU_LEVEL_WHICH,
+                        libc::CPU_WHICH_PID,
+                        -1,
+                        size_of::<libc::cpuset_t>(),
+                        &mut set,
+                    ) == 0
+                    {
+                        let count = libc::CPU_COUNT(&set) as usize;
+                        if count > 0 {
+                            return Ok(NonZero::new_unchecked(count));
+                        }
+                    }
+                }
+            }
+
             #[cfg(target_os = "netbsd")]
             {
                 unsafe {