build samurai with Cosmopolitan Libc

[ahgamut]

This PR adds a Github Action to build samu with Cosmopolitan Libc (cc @jart) when a new tag/release is created.

The result of the action is samu.zip, that contains samu.com, a fat binary that works on x86_64/aarch64, and debug ELF binaries. You can see it here: https://github.com/ahgamut/samurai/releases/tag/untagged-c654d227e531f9e3235f (edit: https://github.com/ahgamut/samurai/releases/tag/1.2-cosmo)

[eli-schwartz]

This seems like a rather large amount of effort to go to just for a non-portable binary that only runs on two of the most common Linux arches. Isn't the whole point of cosmopolitan libc to be, well, portable anywhere?

Would be more impressive if it actually lived up to its name.

[jart]

@ahgamut Is it possible to build this project using just cosmocc -O -o samurai *.c *.cc?

[ahgamut]

Ok, now it builds with just cosmocc, and the built binary samu should work on x86_64 (Linux/BSDs/Windows/MacOS) and aarch64 (Linux/MacOS).