Merge pull request #4851 from rerpha/compiler_warnings_in_core_arm

Fixing some compiler warnings in core/arm/

src/core/arm/dynarmic/arm_dynarmic.h

@@ -17,7 +17,7 @@ class MemorySystem;
 } // namespace Memory
 
 namespace Core {
-struct System;
+class System;
 }
 
 class DynarmicUserCallbacks;

src/core/arm/dyncom/arm_dyncom.h

@@ -11,7 +11,7 @@
 #include "core/arm/skyeye_common/armstate.h"
 
 namespace Core {
-struct System;
+class System;
 }
 
 namespace Memory {