std: Favor cfg! over #[cfg] in unix rwlocks

Author: alexcrichton

src/libstd/sys/unix/rwlock.rs

@@ -49,21 +49,16 @@ impl RWLock {
     #[inline]
     pub unsafe fn write_unlock(&self) { self.read_unlock() }
     #[inline]
-    #[cfg(not(target_os = "dragonfly"))]
     pub unsafe fn destroy(&self) {
-        let r = ffi::pthread_rwlock_destroy(self.inner.get());
-        debug_assert_eq!(r, 0);
-    }
-
-    #[inline]
-    #[cfg(target_os = "dragonfly")]
-    pub unsafe fn destroy(&self) {
-        use libc;
         let r = ffi::pthread_rwlock_destroy(self.inner.get());
         // On DragonFly pthread_rwlock_destroy() returns EINVAL if called on a
         // rwlock that was just initialized with
         // ffi::PTHREAD_RWLOCK_INITIALIZER. Once it is used (locked/unlocked)
         // or pthread_rwlock_init() is called, this behaviour no longer occurs.
-        debug_assert!(r == 0 || r == libc::EINVAL);
+        if cfg!(target_os = "dragonfly") {
+            debug_assert!(r == 0 || r == libc::EINVAL);
+        } else {
+            debug_assert_eq!(r, 0);
+        }
     }
 }