Rollup merge of rust-lang#76521 - tavianator:fix-pthread-getattr-destroy, r=Amanieu

Fix segfault if pthread_getattr_np fails

glibc [destroys][1] the passed pthread_attr_t if pthread_getattr_np()
fails.  Destroying it again leads to a segfault.  Fix it by only
destroying it on success for glibc.

[1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_getattr_np.c;h=ce437205e41dc05653e435f6188768cccdd91c99;hb=HEAD#l205

Author: Dylan-DPC

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

@@ -294,6 +294,7 @@ pub mod guard {
     unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
         let mut ret = None;
         let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
+        #[cfg(target_os = "freebsd")]
         assert_eq!(libc::pthread_attr_init(&mut attr), 0);
         #[cfg(target_os = "freebsd")]
         let e = libc::pthread_attr_get_np(libc::pthread_self(), &mut attr);
@@ -305,7 +306,9 @@ pub mod guard {
             assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr, &mut stacksize), 0);
             ret = Some(stackaddr);
         }
-        assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+        if e == 0 || cfg!(target_os = "freebsd") {
+            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+        }
         ret
     }
 
@@ -403,6 +406,7 @@ pub mod guard {
     pub unsafe fn current() -> Option<Guard> {
         let mut ret = None;
         let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
+        #[cfg(target_os = "freebsd")]
         assert_eq!(libc::pthread_attr_init(&mut attr), 0);
         #[cfg(target_os = "freebsd")]
         let e = libc::pthread_attr_get_np(libc::pthread_self(), &mut attr);
@@ -446,7 +450,9 @@ pub mod guard {
                 Some(stackaddr..stackaddr + guardsize)
             };
         }
-        assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+        if e == 0 || cfg!(target_os = "freebsd") {
+            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+        }
         ret
     }
 }