openbsd: mutex or cond destroy function could return EINVAL

lib/std/reset_event.zig

@@ -109,9 +109,12 @@ const PosixEvent = struct {
     }
 
     fn deinit(self: *PosixEvent) void {
-        // on dragonfly, *destroy() functions can return EINVAL
+        // on dragonfly or openbsd, *destroy() functions can return EINVAL
         // for statically initialized pthread structures
-        const err = if (builtin.os.tag == .dragonfly) os.EINVAL else 0;
+        const err = if (builtin.os.tag == .dragonfly or builtin.os.tag == .openbsd)
+            os.EINVAL
+        else
+            0;
 
         const retm = c.pthread_mutex_destroy(&self.mutex);
         assert(retm == 0 or retm == err);