dpoker needs a little work first (can't find SDL.h).

This can likely be built on Windows, but since I expect I'll be the
only one supporting this for the forseeable future, get the build I
release in here.

<@Deuce> SyncTERM on MSVC really shouldn't be part of CI since it's not expected to work.
<DigitalMan> why not?
<@Deuce> Because it's not supported.
<@Deuce> So it's not part of the integration path.

The AMD64 platform on FreeBSD is called amd64, not x64.

Let's try just caching the 3rd party stuff.

Try capitalizing Linux tag.

Fix sexpots-linux build issue introduced in previous commit.

Remove archive names (uses build names by default?).
Remove "build-" from build names.

Add Windows build job.

Don't cache .o files. This appears to not work 100% (e.g. it's always rebuilding cryptlib anyway and it failed to re-compile some of libsbbs.so resulting in a link failure).