added missing #ifndef KEYCODE_HEADER to keycode.h

src/keycode.h

@@ -17,6 +17,9 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
+#ifndef KEYCODE_HEADER
+#define KEYCODE_HEADER
+
 #include "common_irrlicht.h"
 
 irr::EKEY_CODE keyname_to_keycode(const char *name);
@@ -24,4 +27,5 @@ irr::EKEY_CODE keyname_to_keycode(const char *name);
 // Key configuration getter
 irr::EKEY_CODE getKeySetting(const char *settingname);
 
+#endif