msvcp140: implement _To_byte

[Stefan Dösinger]

Am 2017-07-09 um 13:17 schrieb Henri Verbeet:
> Well, kind of. These are actually from the Presentation Forms-B block.
> I'm not sure why those would be especially relevant for the function
> in question though.
I guess Mikhail picked the first one because it looks like a smiley :-).
All chars produce the default character ('?') on my German Windows
installations, which is a reasonable thing to test.

I guess adding some control characters and undefined utf16 values
similarly to the _To_wide tests may be a good idea.