Code quality: Fix header guards consistency

Adds `header_guards.sh` bash script, used in CI to validate future
changes. Can be run locally to fix invalid header guards.

drivers/coreaudio/audio_driver_coreaudio.h

@@ -28,11 +28,11 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifdef COREAUDIO_ENABLED
-
 #ifndef AUDIO_DRIVER_COREAUDIO_H
 #define AUDIO_DRIVER_COREAUDIO_H
 
+#ifdef COREAUDIO_ENABLED
+
 #include "servers/audio_server.h"
 
 #import <AudioUnit/AudioUnit.h>
@@ -120,6 +120,6 @@ public:
 	~AudioDriverCoreAudio() {}
 };
 
-#endif
+#endif // COREAUDIO_ENABLED
 
-#endif
+#endif // AUDIO_DRIVER_COREAUDIO_H