Style: Replace header guards with #pragma once

core/os/mutex.h

@@ -28,8 +28,7 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
 /**************************************************************************/
 
-#ifndef MUTEX_H
-#define MUTEX_H
+#pragma once
 
 #include "core/typedefs.h"
 
@@ -127,5 +126,3 @@ using Mutex = MutexImpl;
 using BinaryMutex = MutexImpl;
 
 #endif // THREADS_ENABLED
-
-#endif // MUTEX_H