Replace all include guard ifdefs with "#pragma once"

Source/Core/VideoCommon/VideoCommon.h

@@ -2,8 +2,7 @@
 // Licensed under GPLv2
 // Refer to the license.txt file included.
 
-#ifndef _VIDEOCOMMON_H
-#define _VIDEOCOMMON_H
+#pragma once
 
 #ifdef _WIN32
 #define WIN32_LEAN_AND_MEAN
@@ -132,5 +131,3 @@ inline unsigned int GetPow2(unsigned int val)
 		++ret;
 	return ret;
 }
-
-#endif  // _VIDEOCOMMON_H