- 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/p_udmf.cpp

@@ -294,7 +294,7 @@ void P_ClearUDMFKeys()
 	}
 }
 
-static int STACK_ARGS udmfcmp(const void *a, const void *b)
+static int udmfcmp(const void *a, const void *b)
 {
 	FUDMFKey *A = (FUDMFKey*)a;
 	FUDMFKey *B = (FUDMFKey*)b;