(WIDE_CHAR_SUPPORT): New macro.

(WIDE_CHAR_SUPPORT): New macro.
(btowc, iswctype, wctype) [_LIBC]: Redefine to __<fun>.
(BIT_ALPHA, BIT_ALNUM, BIT_ASCII, BIT_NONASCII, BIT_GRAPH, BIT_PRINT)
(BIT_UNIBYTE): Remove.
(re_match_2_internal): Delete corresponding code and streamline the
BIT_MULTIBYTE case to not bother checking ISUNIBYTE.
(CHAR_CLASS_MAX_LENGTH) [!WIDE_CHAR_SUPPORT]: Set to 9 rather than 6.
(re_wctype_t): New type.
(re_wctype, re_iswctype, re_wctype_to_bit): New functions.
(regex_compile): Use them and fix handling of overly long char classes.