Lose Apple branch of SDL_include and prefer non-system headers

sc2/src/port.h

@@ -462,11 +462,7 @@ typedef unsigned int wint_t;
 
 // Use SDL_INCLUDE to portably include the SDL files from the right location.
 // The SDL_DIR definition is provided by the build configuration.
-#ifdef __APPLE__
-#	define SDL_INCLUDE(file) <SDL_DIR/file>
-#else
-#	define SDL_INCLUDE(file) <file>
-#endif  /* SDL_DIR */
+#define SDL_INCLUDE(file) #file
 
 // Mark a function as using printf-style function arguments, so that
 // extra consistency checks can be made by the compiler.