Check the SDL_VIDEO_RENDER_??? macros with #if instead of #ifdef

Allows users to disable them by defining them as 0.

Closes https://github.com/libsdl-org/SDL/issues/8996

(manual port of https://github.com/libsdl-org/SDL/pull/9063 to SDL3.0)

src/render/software/SDL_triangle.c

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_VIDEO_RENDER_SW && !defined(SDL_RENDER_DISABLED)
+#if SDL_VIDEO_RENDER_SW
 
 #include <limits.h>
 
@@ -934,4 +934,4 @@ static void SDL_BlitTriangle_Slow(SDL_BlitInfo *info,
     TRIANGLE_END_LOOP
 }
 
-#endif /* SDL_VIDEO_RENDER_SW && !SDL_RENDER_DISABLED */
+#endif /* SDL_VIDEO_RENDER_SW */