fix hyperroid builds

- add cap guards where necessary
- adapt to new `shiftpoint` datatype and function interfaces thereof

sky.cpp

@@ -447,7 +447,9 @@ EX void make_air() {
     if(vid.antialias & AA_LINES)
       glEnable(GL_LINE_SMOOTH);
 
+#if CAP_SDL
     if(anyshiftclick) IMAGESAVE(airbuf->render(), "air.png");
+#endif
     rb.reset();
     }