Common: Move header guards over to pragma once

Also replaced C headers with the C++ equivalent ones

src/common/memory_util.h

@@ -2,9 +2,7 @@
 // Licensed under GPLv2
 // Refer to the license.txt file included.
 
-
-#ifndef _MEMORYUTIL_H
-#define _MEMORYUTIL_H
+#pragma once
 
 #ifndef _WIN32
 #include <sys/mman.h>
@@ -21,5 +19,3 @@ void UnWriteProtectMemory(void* ptr, size_t size, bool allowExecute = false);
 std::string MemUsage();
 
 inline int GetPageSize() { return 4096; }
-
-#endif