Various code fixes to allow stricter warn flags

[SamantazFox]

When I tried to compile this with CircuitPython (MP fork), I encountered a lot of compilation errors, notably due to missing void in function prototypes and declarations when those take no arguments.

This PR addresses that.

---

Error summary

Encountered a few thousand times in generated lv_mpy.c:

build/lvgl/lv_mpy.c: In function 'get_mp_lv_event_dsc_t_type':
build/lvgl/lv_mpy.c:13923:36: error: old-style function definition [-Werror=old-style-definition]
13923 | static inline const mp_obj_type_t *get_mp_lv_event_dsc_t_type()
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated due to -fmax-errors=50.

Strict/missing prototypes:

In file included from user_modules/lvgl_mpy/lvgl/src/lv_conf_internal.h:56,
                 from user_modules/lvgl_mpy/lvgl/src/lv_init.h:16,
                 from user_modules/lvgl_mpy/lvgl/lvgl.h:21,
                 from build/lvgl/lv_mpy.c:33:
user_modules/lvgl_mpy/lv_conf.h:432:1: error: function declaration isn't a prototype [-Werror=strict-prototypes]
  432 | extern void mp_lv_init_gc();
      | ^~~~~~
user_modules/lvgl_mpy/lv_conf.h:433:1: error: function declaration isn't a prototype [-Werror=strict-prototypes]
  433 | extern void mp_lv_deinit_gc();
      | ^~~~~~
build/lvgl/lv_mpy.c: At top level:
build/lvgl/lv_mpy.c:359:6: error: no previous prototype for 'mp_lv_log_cb' [-Werror=missing-prototypes]
  359 | void mp_lv_log_cb(lv_log_level_t level, const char * buf){
      |      ^~~~~~~~~~~~
build/lvgl/lv_mpy.c:364:6: error: no previous prototype for 'mp_lv_init_gc' [-Werror=missing-prototypes]
  364 | void mp_lv_init_gc(void)
      |      ^~~~~~~~~~~~~
build/lvgl/lv_mpy.c:373:6: error: no previous prototype for 'mp_lv_deinit_gc' [-Werror=missing-prototypes]
  373 | void mp_lv_deinit_gc(void)
      |      ^~~~~~~~~~~~~~~
build/lvgl/lv_mpy.c: In function 'mp_mp_lv_init_gc':
build/lvgl/lv_mpy.c:41561:5: error: function declaration isn't a prototype [-Werror=strict-prototypes]
41561 |     ((void (*)())lv_func_ptr)();
      |     ^

Shadowed variable:

build/lvgl/lv_mpy.c: In function 'lv_to_mp':
build/lvgl/lv_mpy.c:249:31: error: declaration of 'lv_obj_class' shadows a global declaration [-Werror=shadow]
  249 |         const lv_obj_class_t *lv_obj_class = lv_obj_get_class(lv_obj);
      |                               ^~~~~~~~~~~~
In file included from user_modules/lvgl_mpy/lvgl/lvgl.h:43:
user_modules/lvgl_mpy/lvgl/src/core/lv_obj.h:218:54: note: shadowed declaration is here
  218 | LV_ATTRIBUTE_EXTERN_DATA extern const lv_obj_class_t lv_obj_class;
      |                                                      ^~~~~~~~~~~~

[cubic-dev-ai]

No issues found across 2 files