Add support for x86_64-fortanix-unknown-sgx target

[akash-fortanix]

The x86_64-fortanix-unknown-sgx recently gained Tier 3 support upstream.

[jethrogb]

@dingelish are you changing your target as suggested so that it's no longer cfg(unix)?

[jethrogb]

Build failures come from building using a compiler in CI that's either too old or too new.

[dingelish]

Hi @jethrogb ,

Not finished yet. I just look into the build failure. The log says:

22.88s$ cargo build --verbose
    Updating registry `https://github.com/rust-lang/crates.io-index`
Failed to parse registry's information for: rand
Caused by:
  the given version requirement is invalid
The command "cargo build --verbose" exited with 101.
0.50s$ cargo test --verbose
    Updating registry `https://github.com/rust-lang/crates.io-index`
Failed to parse registry's information for: rand
Caused by:
  the given version requirement is invalid
The command "cargo test --verbose" exited with 101.
0.50s$ cargo doc --no-deps
    Updating registry `https://github.com/rust-lang/crates.io-index`
An unknown error occurred
To learn more, run the command again with --verbose.
The command "cargo doc --no-deps" exited with 101.

Seems that something around rand is wrong. Any idea?

[jethrogb]

As I said, the compiler is too old, looks like the cargo that's distributed with Rust 1.0.0 no longer works with the current crates.io.