Add openssl as a dependency for cmake when building cmake from source

[jsharpe]

Update cmake build to include openssl as a dependency.

Closes #709.

[jsharpe]

@UebelAndre the only issue with this change is that because openssl requires rules_perl then this means we'd need to move to a two phase initialisation in the WORKSPACE to be able to call the rules_perl setup functions unless you can think of a way to avoid this?

[UebelAndre]

I think that's an appropriate thing to do. The bigger question is do we value the use of rules_perl enough to do that though. I feel like it'd be best to try and build OpenSSL using rules_cc if possible but that's a massive undertaking. Right now rules_perl does not provide windows support which feels like a blocker there. So if that's true, then we'll likely want to maintain the previous way of building OpenSSL when compiling it for the toolchains here

[jsharpe]

Building openssl via rules_cc has been done at dropbox but only for linux x86_64. This PR adds support for macOS dropbox/dbx_build_tools#40 but we'd still be missing windows / other platform support.
I think adding in rules_perl is something that we'll need to do anyway eventually as some of the autotools toolchain requires perl to build; I don't think adding support for windows to it should be that big a deal; afterall we just need it to set the PERL MakeVariable for our use, so even if we add a toolchain for windows that doesn't work with all the rules_perl features I think that'll be ok.