Add pointer cast magic to avoid pedantic warnings with gcc-13

[Gottox]

The same trick is used on line 689, so I'm considering it reasonable to do the same for js_os_exec_once_init.

// ...
// line 689:
    *(void **) (&init) = dlsym(hd, "js_init_module");
// ...

[Gottox]

Would it make sense to run the CI with -Wpedantic -Werror? - afaics quickjs-ng is handling pedantic just fine after this PR with clang-17/gcc-13.

[saghul]

Let's give it a try!