Common: Move header guards over to pragma once

Also replaced C headers with the C++ equivalent ones

src/common/fifo_queue.h

@@ -1,6 +1,4 @@
-
-#ifndef _FIFO_QUEUE_H_
-#define _FIFO_QUEUE_H_
+#pragma once
 
 // a simple lockless thread-safe,
 // single reader, single writer queue
@@ -111,5 +109,3 @@ private:
 };
 
 }
-
-#endif