Enable UTF8 in gnulib regexp.

	Enable UTF8 in gnulib regexp.

	* config.h.in (RE_ENABLE_I18N) [!GRUB_UTIL]: New define.
	* grub-core/lib/posix_wrap/ctype.h (islower): Use grub_islower.
	(isupper): Use grub_isupper.
	(isascii): New inline function.
	* grub-core/lib/posix_wrap/wchar.h: Replace dummy with real contents.
	* grub-core/lib/posix_wrap/wctype.h: Likewise.
	* grub-core/normal/charset.c (grub_utf8_process): New function.
	(grub_utf8_to_utf16): Use grub_utf8_process.
	(grub_encode_utf8_character): New function.
	(grub_ucs4_to_utf8): Use grub_encode_utf8_character.
	* include/grub/charset.h (grub_utf8_process): New declaration.
	(grub_encode_utf8_character): Likewise.
	* include/grub/misc.h (grub_islower): New inline function.
	(grub_isupper): Likewise.
	(grub_strchrsub): Moved down to fix the definitions.