Add tests for double destroying various pthread items

tests/compile-fail/sync/libc_pthread_cond_double_destroy.rs

@@ -0,0 +1,22 @@
+// ignore-windows: No libc on Windows
+#![feature(rustc_private)]
+
+/// Test that destroying a pthread_cond twice fails, even without a check for number validity
+extern crate libc;
+
+fn main() {
+    unsafe {
+        use core::mem::MaybeUninit;
+        let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
+        libc::pthread_condattr_init(attr.as_mut_ptr());
+
+        let mut cond = MaybeUninit::<libc::pthread_cond_t>::uninit();
+
+        libc::pthread_cond_init(cond.as_mut_ptr(), attr.as_ptr());
+
+        libc::pthread_cond_destroy(cond.as_mut_ptr());
+
+        libc::pthread_cond_destroy(cond.as_mut_ptr());
+        //~^ Undefined Behavior: using uninitialized data, but this operation requires initialized memory
+    }
+}

tests/compile-fail/sync/libc_pthread_mutex_double_destroy.rs

@@ -0,0 +1,23 @@
+// ignore-windows: No libc on Windows
+#![feature(rustc_private)]
+
+/// Test that destroying a pthread_mutex twice fails, even without a check for number validity
+extern crate libc;
+
+fn main() {
+    unsafe {
+        use core::mem::MaybeUninit;
+
+        let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
+        libc::pthread_mutexattr_init(attr.as_mut_ptr());
+
+        let mut mutex = MaybeUninit::<libc::pthread_mutex_t>::uninit();
+
+        libc::pthread_mutex_init(mutex.as_mut_ptr(), attr.as_ptr());
+
+        libc::pthread_mutex_destroy(mutex.as_mut_ptr());
+
+        libc::pthread_mutex_destroy(mutex.as_mut_ptr());
+        //~^ Undefined Behavior: using uninitialized data, but this operation requires initialized memory
+    }
+}

tests/compile-fail/sync/libc_pthread_mutexattr_double_destroy.rs

@@ -0,0 +1,19 @@
+// ignore-windows: No libc on Windows
+#![feature(rustc_private)]
+
+/// Test that destroying a pthread_mutexattr twice fails, even without a check for number validity
+extern crate libc;
+
+fn main() {
+    unsafe {
+        use core::mem::MaybeUninit;
+        let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
+
+        libc::pthread_mutexattr_init(attr.as_mut_ptr());
+
+        libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
+
+        libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
+        //~^ Undefined Behavior: using uninitialized data, but this operation requires initialized memory
+    }
+}

tests/compile-fail/sync/libc_pthread_rwlock_double_destroy.rs

@@ -0,0 +1,16 @@
+// ignore-windows: No libc on Windows
+#![feature(rustc_private)]
+
+/// Test that destroying a pthread_rwlock twice fails, even without a check for number validity
+extern crate libc;
+
+fn main() {
+    unsafe {
+        let mut lock = libc::PTHREAD_RWLOCK_INITIALIZER;
+
+        libc::pthread_rwlock_destroy(&mut lock);
+
+        libc::pthread_rwlock_destroy(&mut lock);
+        //~^ Undefined Behavior: using uninitialized data, but this operation requires initialized memory
+    }
+}