Allow using multiplatform images

[larskanis]

These are the changes necessary to build both linux/amd64 and linux/arm64 docker images. This way we can provide not only images running on x86_64 but also aarch64. They run much faster on ARM based Mac and ARM based Linux systems.

On the native platform (x86_64-linux or aarch64-linux) ruby configure script finds libz and libcrypt and makes use of it in libruby.
Disabling them per ac_cv_* variables unifies cross builds and we can remove platform specific injection of -lz and -lcrypt into mkmf.rb .

The docker image for the x64-mingw-ucrt compiler larskanis/mingw64-ucrt needs to be rebuilt on linux/arm64 platform, so that both arm64 and amd64 are provided. Currently the image for platform linux/amd64 is used on linux/arm64, which doesn't work.

The rebuild fails on docker arm64 emulation with segmentation fault, but works flawlessly on a real arm64 device.
When it is rebuilt, the deb package versions have changed versions, which is adjusted below. So it makes sense to rebuild and push larskanis/mingw64-ucrt just before this PR is merged.

I didn't test whether the image build on x86_64 with docker buildx arm64 emulation works. Maybe they crash similar to mingw64-ucrt. In any case it's very slow. However I can build the linux/arm64 images locally and push them manually.

Fixes #78

[flavorjones]

@larskanis I don't think this PR is enough to completely close #78 since we probably need to figure out a way to build and ship these reliably (maybe using Github Actions for reproducibility)?

[larskanis]

Thank you Mike for your review! I merged it to get forward with the ARM64 support at least locally. I'll try to make the images available for both architectures. Reopened #78 for now.