uclibc insists on having 70k static buffer for crypt.

For bbox it's not acceptable. Roll our own des and md5 crypt
implementation. Against older uclibc:

   text    data     bss     dec     hex filename
 759945     604    6684  767233   bb501 busybox_old
 759766     604    6684  767054   bb44e busybox_unstripped

so, we still save on code size.

libbb/correct_password.c

@@ -71,7 +71,7 @@ int correct_password(const struct passwd *pw)
 	if (!unencrypted) {
 		return 0;
 	}
-	encrypted = crypt(unencrypted, correct);
+	encrypted = pw_encrypt(unencrypted, correct, 1);
 	memset(unencrypted, 0, strlen(unencrypted));
 	return strcmp(encrypted, correct) == 0;
 }