Added support for wasm32-wasi target

[OtaK]

Hi!

I'm currently on my way to make SQLite work with wasm32-wasi. So, one of the blockers was OpenSSL in general since SQLite depends heavily on it.

Here's my shot at it:

• Introduces no new dependencies
• Small alteration of the docker test harness to:
  • install wasmtime & set it up as test runner
  • install & setup wasi-sdk
• Compatible with all versions of OpenSSL (1.1.x and 3.x.x were tested).

This should be the first step in closing https://github.com/sfackler/rust-openssl/issues/1016

Should also supersede #113

Please give me any feedback! I'll tend to it ASAP.

[alexcrichton]

Ah ok sorry I didn't realize that this wasn't passing CI, I'll take another look when CI is passing for wasm32-wasi

[alexcrichton]

Looks good to me, thanks!