Change RGB32k to a union of BYTE[32][32][32] and BYTE[32*32*32]

- Clang's optional runtime array bounds checking doesn't understand when we
  intentionally "overflow" by doing this:
    RGB32k[0][0][colorval]
  It will warn that it was accessed at an index will past the bounds
  of type 'BYTE [32]', which makes it less than useful for catching real
  array bounds overflows. So now do this:
    RGB32k.All[colorval]
  And if you want this:
    RGB32k[r][g][b]
  Now do this:
    RGB32k.RGB[r][g][b]

src/textures/pcxtexture.cpp

@@ -528,7 +528,7 @@ void FPCXTexture::MakeTexture()
 		{
 			for(int x=0; x < Width; x++)
 			{
-				Pixels[y+Height*x] = RGB32k[row[0]>>3][row[1]>>3][row[2]>>3];
+				Pixels[y+Height*x] = RGB32k.RGB[row[0]>>3][row[1]>>3][row[2]>>3];
 				row+=3;
 			}
 		}