kconfig: error out when seeing recursive dependency

Originally, recursive dependency was a fatal error for Kconfig
because Kconfig cannot compute symbol values in such a situation.

Commit d595cea624 ("kconfig: print more info when we see a recursive
dependency") changed it to a warning, which I guess was not intentional.

Get it back to an error again.

Also, rename the unit test directory "warn_recursive_dep" to
"err_recursive_dep" so that it matches to the behavior.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Dirk Gouders <dirk@gouders.net>

scripts/kconfig/symbol.c

@@ -1248,9 +1248,6 @@ struct symbol *sym_check_deps(struct symbol *sym)
 		sym->flags &= ~SYMBOL_CHECK;
 	}
 
-	if (sym2 && sym2 == sym)
-		sym2 = NULL;
-
 	return sym2;
 }