sub my_func
{
    my( $string, $int, @strings )= @_;
    my $ptrs= pack "P" x @strings, @strings;
    $ptrs .= pack "LL", 0, 0; # For odd systems with sizeof(IV) < sizeof(void *)
    _my_func( $string, $int, $ptrs );
}

# and

void
_my_func( st­ring, integer, strings )
    const char * string
    int          integer
    char *       strings
CODE:
    my_func( string, integer, (char **)(strings) );