Cygwin: fnmatch: support collating symbols in [. .] brackets

Cygwin: fnmatch: support collating symbols in [. .] brackets

This requires quite a few changes in how fnmatch operates.
It always operates on wint_t strings now, just like regex and glob,
and it always keeps a pointer on the character inside the string,
rather than operating on a single character.

As a result, just drop the ifdef's for Cygwin.  The code is
non-portable now anyway...

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>