use SDL stdlib where possible

include/twn_util.h

@@ -7,11 +7,8 @@
 #include <SDL2/SDL.h>
 #include <physfs.h>
 
-#include <stdlib.h>
 #include <stdint.h>
 #include <stdbool.h>
-#include <math.h>
-#include <stdnoreturn.h>
 
 
 /*                   */
@@ -31,7 +28,7 @@ TWN_API void log_warn(const char *restrict format, ...);
 
 
 /* for when there's absolutely no way to continue */
-TWN_API noreturn void die_abruptly(void);
+TWN_API _Noreturn void die_abruptly(void);
 
 
 /* "critical" allocation functions which will log and abort() on failure. */