If I understood you correctly use function prototypes:

void init_menu();

void init_game()
{
init_menu();
...
}

Then define the content of the init_menu declaration later as if you would have never used such a prototype, so:

void init_menu()
{
...
}

The parameters and the return type have to match, thus the prototyp to

var ent_get_dist(ENTITY* ent, VECTOR* vtarget) {...}

is

var ent_get_dist(ENTITY*, VECTOR*);