Moving openssl to one of the everest sub-projects

[darrenge]

From @protz

There is one bit of work that we could use some help with. Currently, several projects depend on OpenSSL, but the way we track OpenSSL is a little bit... makeshift, to say the least. Currently, both F and HACL have an OpenSSL git submodule, which is manually updated once in a while. The reason we'd like to move away from this setup is manifold:

• first, it'd be great to get everyone on the same page
• second, we keep shooting ourselves in the foot, as git submodules require one to remember to run "git submodule update" after each branch switch (failure to do that means a spurious revert to an old version of OpenSSL)
• third, it is a dependency of Everest, and as such, probably deserves the same treatment as the other tools.

I envision a modification of hashes.sh inside of project-everest/everest to also track OpenSSL, and update it regularly just like the other tools. The only bit that would be different is that the first clone would be followed by a configure invocation that currently depends on the platform (see https://github.com/FStarLang/FStar/blob/master/ucontrib/CoreCrypto/ml/Makefile#L25 where we currently do this). After that, it would just be a matter of running git pull followed by make -C openssl.

The CI for miTLS and HACL* would then be a little bit different: we would do what we currently do for Kremlin/Vale, that is, get the latest hashes.sh to know which revision of OpenSSL to use, then build & export OPENSSL_HOME accordingly

[s-zanella]

We now have single checkout of OpenSSL tracked in MLCrypto and used for CI. hacl-star@master still has an OpenSSL submodule, but we are mainly using hacl-star@fstar-master which doesn't have it.