tolower_l
int tolower_l(int, locale_t);
# define TOLOWER(Ch) tolower_l ((unsigned char) (Ch), loc)
while (tolower_l(*us1, locale) == tolower_l(*us2++, locale))
return (tolower_l(*us1, locale) - tolower_l(*--us2, locale));
if (tolower_l(*us1, locale) != tolower_l(*us2++, locale))
return (tolower_l(*us1, locale) - tolower_l(*--us2, locale));