LC_TIME locale category. Conditionalize using _WANT_C99_TIME_FORMATS
flag.
(STRTOUL): Define differently for building strftime or wcsftime.
(STRCPY): Ditto.
(STRCHR): Ditto.
(STRLEN): Ditto.
(CHECK_LENGTH): Define to simplify code.
(era_info_t): New type to store era info.
(get_era_info): New function to fetch era info matching incoming
struct tm.
(free_era_info): New function to free era info.
(alt_digits_t): New type to store alternative digits.
(get_alt_digits): New function to convert alt_digits string into
alt_digits_t structure.
(free_alt_digits): New function to free alt_digits info.
(conv_to_alt_digits): New function to convert unsigned value into
alternative digits.
(strftime): Conditionalize on _WANT_C99_TIME_FORMATS. If
_WANT_C99_TIME_FORMATS is defined, define as just a wrapper function
providing era_info and alt_digits pointers and call ...
(__strftime): Rename from strftime and make static if
_WANT_C99_TIME_FORMATS is defined. Add parameters for era_info and
alt_digits pointers. Handle conversion modifiers according to
POSIX-1.2008. Redefine %F and %Y according to POSIX. Add default case
to allow to bail out on invalid conversion specifiers.
* libc/include/sys/config.h: Move Cygwin build flags to Cygwin's
config.h.
* libc/include/stdio.h: Remove __CYGWIN_USE_BIG_TYPES__ condition.