add support for setreuid/setregid and exculde a false positive

[9iang22]

I found that the following case will be reported by raptor-incorrect-order-setuid-setgid, the root cause is that the rule only has a whitelist for the pattern to recover the root privilege with seteuid(0).

void temp_priv_drop_safe()
{
	uid_t saved_uid;
	struct passwd *pwd;

	// ok: raptor-incorrect-order-setuid-setgid
	saved_uid = geteuid();
	pwd = getpwnam("nobody");
	if (pwd != NULL) {
		(void)seteuid(pwd->pw_uid);
		/* do unprivileged work */
		FILE *fp = fopen("/tmp/unpriv_file.txt", "r");
		if (fp) fclose(fp);
		/* restore original privileges */
		(void)seteuid(saved_uid);
	}
}

The following pattern will help:

          - pattern-not-inside: |
              $UID = geteuid();
              ...
              <... seteuid($UID) ...>;

Also, the rule now does not support the setreuid/setregid order reverse.

I'd like to open a pr for these if you think they should be improved.