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_tools.h

@@ -19,7 +19,7 @@
 
 #include "../libs/lvgl/lvgl.h"
 
-lv_obj_t *ums_mbox;
+extern lv_obj_t *ums_mbox;
 
 void create_tab_tools(lv_theme_t *th, lv_obj_t *parent);
 void nyx_run_ums(void *param);