Fix scan-build warnings about assigning to char**
scan-build complains about: tor_check_port_forwarding:
const char **argv; /* cli arguments */ ... argv = tor_calloc(args_n, sizeof(char *));
process_environment_t *env = tor_malloc_zero(sizeof(process_environment_t)); ... env->unixoid_environment_block = tor_calloc(n_env_vars + 1, sizeof(char *));
This is fine, and maybe there's a cast or magic comment we could use to make the warnings go away.