kconfig: do not record timestamp in .config

If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not

break symlinks when .config is a symlink to somewhere else.

KCONFIG_NOTIMESTAMP

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If this environment variable exists and is non-null, the timestamp line

in generated .config files is omitted.

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Environment variables for '{allyes/allmod/allno/rand}config'

	const char *basename;

	const char *str;

	char dirname[PATH_MAX+1], tmpname[PATH_MAX+1], newname[PATH_MAX+1];

	time_t now;

	int use_timestamp = 1;

	char *env;

	dirname[0] = 0;

	if (!out)

		return 1;

	time(&now);

	env = getenv("KCONFIG_NOTIMESTAMP");

	if (env && *env)

		use_timestamp = 0;

	fprintf(out, _("#\n"

		       "# Automatically generated make config: don't edit\n"

		       "# %s\n"

		       "%s%s"

		       "#\n"),

		     rootmenu.prompt->text,

		     use_timestamp ? "# " : "",

		     use_timestamp ? ctime(&now) : "");

		     rootmenu.prompt->text);

	if (!conf_get_changed())

		sym_clear_all_valid();