Fix some compilation errors in windows.cpp

[chrchr-github]

_strncpy_s_l() is apparently only available in non-unicode builds, but the other code relies on UNICODE.

[firewave]

Do you still plan to address some of the compiler warnings? Otherwise I would merge it.

If you want the warnings to be errors you need to add the /WX switch.

I was thinking about adding it to runtests.sh by using the MinGW cross-compilation. That can still be done later on.

The UNICODE handling needs some reworking. No tickets about that but some stuff is sprinkled around in several PRs and branches of mine...

[chrchr-github]

The warnings are to be expected, since the test code is obviously flawed. We could try to suppress them with /w, but I don't quite see the point.