Compiler: Rename __forceinline define to DOLPHIN_FORCE_INLINE

This is much better as prefixed double underscores are reserved for the
implementation when it comes to identifiers. Another reason its better,
is that, on Windows, where __forceinline is a compiler built-in, with
the previous define, header inclusion software that detects unnecessary
includes will erroneously flag usages of Compiler.h as unnecessary
(despite being necessary on other platforms). So we define a macro
that's used by Windows and other platforms to ensure this doesn't
happen.

Source/Core/Common/ChunkFile.h

@@ -257,7 +257,7 @@ private:
     DoEachElement(x, [](PointerWrap& p, typename T::value_type& elem) { p.Do(elem); });
   }
 
-  __forceinline void DoVoid(void* data, u32 size)
+  DOLPHIN_FORCE_INLINE void DoVoid(void* data, u32 size)
   {
     switch (mode)
     {