Fix sccache usage in Windows CI builds

[jherico]

Description

This corrects a couple problems preventing the Windows CI builds from using sccache.

Fix for #896 and reduces windows build significantly.

[jherico]

@gpx1000 You mentioned having trouble getting sccache working in Windows CI builds. I was able to track it down after I noticed something odd in the beginning of the CMake config.

The basic issue was twofold...

• Although sccache doesn't work with the Visual Studio generator, some sources online seem to suggest it works with the "NMake Makefiles" generator, but as far as I can tell it does not. Switching to Ninja works though.
• The online commentary about the need to use /Z7 instead of /Zi may be accurate, but the mechanism that was being used didn't work for the reasons I noted in CMake configuration order of operations is incorrect #896

[tomadamatkinson]

Nice! Looks like this cuts the Windows build down from ~30minutes to ~7minutes in the CI

[jherico]

It occurred to me that I should revert the change adding messaging about lack of ccache or sccache since they don't work with the most commonly used Windows generators. I could gate them behind a if (CMAKE_GENERATOR MATCHES "Visual Studio"), but I figured it's best to just leave it closer to as is.

[gpx1000]

I always kept it in Ninja build for Windows as I wanted to ensure the windows build system was using at least NMake. SCCache was supposed to work with NMake but I never got that working right. I think it's far better to just bite the bullet and use Ninja as you have here. I don't think at first blush that the macos build failure in CI is due to the changes here. lemme know if you need help changing it.
Thanks for the contribution; greatly appreciated! And great catches of bugs.

[SaschaWillems]

Thank you very much for this PR. Works fine for me on Windows 11 👍🏻

[gpx1000]

lgtm; thanks for the contribution!