Document missing dependency (gcc-multilib) for Ubuntu setup

[sbellem]

Problem encountered when trying to build cipher-paratime with SGX support.

See oasisprotocol/cipher-paratime#19 for more details.

I don't know what the equivalent is for Fedora systems. I'll add it once I find out.

[tjanez]

@sbellem, thanks for your pull request!

Problem encountered when trying to build cipher-paratime with SGX support.

See oasisprotocol/cipher-paratime#19 for more details.

Indeed, this is required when building the Cipher ParaTime SGX binary on Ubuntu/Debian systems.

We've now augmented the Cipher ParaTime Building instructions in oasisprotocol/cipher-paratime#34.

I don't know what the equivalent is for Fedora systems. I'll add it once I find out.

It turns out Fedora doesn't need any additional packages for that.

However, even though gcc-multilib was initially only required for building the Cipher ParaTime SGX binary, in #4789, the oasis-core-runtime binary started depending on the mbedtls crate:

oasis-core/runtime/Cargo.toml

Line 26 in 940edde

mbedtls = "0.8.1"

And mbedtls also requires the gcc-multilib package being installed on Ubuntu/Debian systems when building oasis-core-runtime.

[sbellem]

Thanks @tjanez!