msvcrt: Add support for sprintf_s

[Jason Edmeades]

>This doesn't seem correct to me

You are right, its incomplete, but it also was based on the logic
already in MSVCRT_vswprintf_s, which is just as incomplete!

I'll happily just raise a bug report if the patch is insufficient, but
in general all the _s special processing is missing from the printf*
family, and the patch implements enough to get the basic functionality
working. I probably should have put a fixme comment in like
MSVCRT_vswprintf_s though but would that be enough?

Jason