build hello fw with GCC Toolchain v2020.04.1 (set GPIO_IOF_EN). Remove obsolete function write_hex

hello/bsp/libwrap/sys/_exit.c

@@ -10,7 +10,6 @@ void __wrap__exit(int code)
 //*leds = (~(code));
 
   write(STDERR_FILENO, message, sizeof(message) - 1);
-  write_hex(STDERR_FILENO, code);
   write(STDERR_FILENO, "\n", 1);
 
   for (;;);