[newlib-cygwin] scanf: allow hex float input per POSIX

[Corinna Vinschen]

Hi folks,

I just pushed a patch which adds support for hex float values per POSIX
to our scanf code.  Given how scanf is a bit convoluted, I'd be grateful
if some kind soul could review my patch and ask nagging question, if so
inclined.

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=9c6c2fb0f697e70f1d1eacad915ea5f76bb123e6


Thanks,
Corinna