newlib: [w]scanf: Fix behaviour on matching failure
The special handling of %\0 in [w]scanf is flawed. It's just a
matching failure and should be handled as such. scanf also
fakes an int input value on %X with X being an invalid conversion
char. This is also just a matching failure and should be handled
the same way as %\0.
There's no indication of the reason for this "disgusting
backwards compatibility hacks" in the logs, given this
code made it into newlib before setting up the CVS repo.
Just handle these cases identically as matching failures.