fixes for compiling with gcc 10

gcc 10 no longer lets you get away with not externing global variables in header files. This adds the necessary extern and adds defines in appropriate c files

nyx/nyx_gui/frontend/gui_emmc_tools.c

@@ -39,6 +39,8 @@ extern hekate_config h_cfg;
 
 extern void emmcsn_path_impl(char *path, char *sub_dir, char *filename, sdmmc_storage_t *storage);
 
+lv_obj_t *ums_mbox;
+
 typedef struct _emmc_backup_buttons_t
 {
 	lv_obj_t *emmc_boot;