locale: more output fixes
- make abday, day, abmon, mon, am_pm output quoting match linux
- workaround localeconv() issue for mon_grouping and grouping (PR172215)
- for other values not available in default locale, output -1 instead of 127 (CHAR_MAX) as returned by localeconv()
With these changes, output of locale and locale -k for all keywords
specified by POSIX exactly matches the linux one.