Rollup merge of rust-lang#132607 - YohDeadfall:pthread-name-fn-with-result, r=tgross35

Used pthread name functions returning result for FreeBSD and DragonFly

`pthread_getname_np` and `pthread_setname_np` received a wider adoption in past years and was added to:
* FreeBSD by June 11 2020 via [`2ef84b7da9a6c3e23b4a135e6e863581f16d46e1`](freebsd/freebsd-src@2ef84b7),
* DargonFly by March 8 2021 via [`ab5dc9aceb34419d1c4b6006739e61acee8ee999`](https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ab5dc9aceb34419d1c4b6006739e61acee8ee999).

There's not so much advantage except that the result can be checked in debug builds. Ideally it should be unified with Linux' implementation, but it trims the input.

Author: matthiaskrgr

Diff for: library/std/src/sys/pal/unix/thread.rs

@@ -130,25 +130,28 @@ impl Thread {
         }
     }
 
-    #[cfg(target_os = "linux")]
+    #[cfg(any(target_os = "linux", target_os = "freebsd", target_os = "dragonfly"))]
     pub fn set_name(name: &CStr) {
-        const TASK_COMM_LEN: usize = 16;
-
         unsafe {
-            // Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20.
-            let name = truncate_cstr::<{ TASK_COMM_LEN }>(name);
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "linux")] {
+                    // Linux limits the allowed length of the name.
+                    const TASK_COMM_LEN: usize = 16;
+                    let name = &truncate_cstr::<{ TASK_COMM_LEN }>(name);
+                } else {
+                    // FreeBSD and DragonFly BSD do not enforce length limits.
+                    let name = name.to_bytes();
+                }
+            };
+            // Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20 for Linux,
+            // FreeBSD 12.2 and 13.0, and DragonFly BSD 6.0.
             let res = libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
             // We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
             debug_assert_eq!(res, 0);
         }
     }
 
-    #[cfg(any(
-        target_os = "freebsd",
-        target_os = "dragonfly",
-        target_os = "openbsd",
-        target_os = "nuttx"
-    ))]
+    #[cfg(any(target_os = "openbsd", target_os = "nuttx"))]
     pub fn set_name(name: &CStr) {
         unsafe {
             libc::pthread_set_name_np(libc::pthread_self(), name.as_ptr());