[FR] Build Windows binaries with DoH support.

[gitbaby-afk]

Unbound works as DoH server on Linux since it is compiled with libnghttp2 by default (at least on some distros).
I tested it and building and running unbound with DoH on Windows seems to work. But I did not test it a lot.
Would it be possible to build the Windows binaries with DoH by default, too?
(iirc the Windows build instructions could also need some minor updates.)

[wcawijngaards]

I fixed some build warnings for the build of DoH on Windows. That is also not with tests, but it compiles nicely.