Allow compiling against OpenSSL on macOS

[pimeys]

We're kind of hit by the issue of Apple's Secure Transport being super picky about certificates since macOS Catalina in Tiberius. We really can't change how Microsoft creates their certificates or what kind of certs Apple accepts. I was thinking could it be possible to force this crate to statically compile against OpenSSL, so we could distribute a version of Prisma for macOS that could talk TLS with SQL Server?

I don't know is this the right solution here, but that's how node.js solved the issues for their users: statically linking to OpenSSL on all platforms.

[yoshuawuyts]

@pimeys if you're willing to write a PR for this, I'd be happy to review it!