Add support for building for Windows ARM64

[ddscentral]

This PR adds support for building libcec for Windows ARM64.

Please also check out the relevant PRs for "platform" and "support" submodules.

Pulse-Eight/platform#50
Pulse-Eight/libcec-support#4

[garbear]

I went through all commits of all 3 PRs, and it looks like the port was done correctly. I saw no surprises.

I haven't compiled tested yet, will try to do so once I get my Windows system backup and running.

[anthony-linaro]

Is libcecsharp included in this too, or is the intention to build without it (or did I clone something wrong?)

I cloned this repo recursively, and use the build command:
windows\build-all.cmd arm64

It then appears to try and build the x64 version of libcecsharp, on my WoA machine

[ddscentral]

It isn't, unfortunately.
I have attempted to get it built (https://github.com/ddscentral/cec-dotnet-win-arm64) as well but there's no compatible .NET SDK for ARM64 which would work.

[anthony-linaro]

No compatible one, as in the ones that support it are too new compared to the one the project requires?

Is there a command line I should be using for building/testing then, that doesn't build libcecsharp?