Build without Win32.mak, and using Universal C Runtime (UCRT)

windows: Check for APPVER, not VCVER for UCRT

When deciding whether UCRT is used (and thus no CRT merge modules), check for
Windows 10 rather than the version of Visual Studio, as we may be building with
an older SDK.

We don't use it anywhere for anything.

Catch overflows that result from adding PAC_INFO_BUFFER_SIZE.

Samba BUG: https://bugzilla.samba.org/show_bug.cgi?id=15203



Signed-off-by: Nico Williams <nico@twosigma.com>