+X11_CFLAGS = $(X11_INCL)
+X11_LDFLAGS = $(X11_LIBS) -lX11
+
+USE_SDL = true
+
+ifdef USE_SDL
+SYS_CFLAGS = $(SDL_CFLAGS)
+SYS_LDFLAGS = $(SDL_LDFLAGS)
+else
+SYS_CFLAGS = $(X11_CFLAGS)
+SYS_LDFLAGS = $(X11_LDFLAGS)
+endif
+
+INCL = $(SYS_CFLAGS)
+LIBS = $(SYS_LDFLAGS) $(EXTRA_LIBS) -lm