WIP: example of implementing external deps for extra platforms

[illwieckz]

My test bed for #1822, so it includes #1822:

• https://github.com/DaemonEngine/Daemon/pull/1822

While I would like to see #1822 merged for the release (it makes releasing easier), those changes aren't needed for the release. There is no urge.

But this way curious people can already know about it and if they want, toy with it.

This adds:

• linux-riscv64-default, I tested building the deps, building the engine and the game dll against the deps, and run both the client and the server and it is working (except there is no nacl support).
• macos-arm64-default, I only tested building the deps (they build), I haven't tested building the engine against them, and then I haven't tested running the engine. The purpose is to make it easier for the user to build a native arm64 engine, only using amd64 binaries for the nacl loader.
• freebsd-amd64-default, the deps build without error but I know OpenAL isn't properly linked, building the linux nacl runtime on FreeBSD is probably an impossible task, so that's more a demo for now. It can probably already be used to build a static server engine to run some native server game code.

[illwieckz]

Some commits are good to get even outside of the effort to enable those platforms, like:

• external_deps: do not cross-compile pkgconfig
• external_deps: rework the macos-amd64 setup a bit
• external_deps: do not build OpenAL utils

But those aren't needed for the release either. They can be merged separately, but there is no urge to do so.