- removed STACK_ARGS.

The only reason this even existed was that ZDoom's original VC projects used __fastcall. The CMake generated project do not, they stick to __cdecl.
Since no performance gain can be seen by using __fastcall the best course of action is to just remove all traces of it from the source and forget that it ever existed.

src/r_data/sprites.cpp

@@ -497,7 +497,7 @@ static const char *skinsoundnames[NUMSKINSOUNDS][2] =
 };
 
 /*
-static int STACK_ARGS skinsorter (const void *a, const void *b)
+static int skinsorter (const void *a, const void *b)
 {
 	return stricmp (((FPlayerSkin *)a)->name, ((FPlayerSkin *)b)->name);
 }