cargo-auditable is incompatible with cargo-capi

[Shnatsel]

Discussed in #175

On https://github.com/rustls/rustls-ffi, cargo auditable capi build produces a shared library without audit data.

The culprit is this line:

cargo-auditable/cargo-auditable/src/rustc_wrapper.rs

Line 25 in ceb4475

if args.print.is_empty()

If I replace it with if true, it works. That's because cargo capi passes both --print and --emit arguments to rustc, which I didn't realize was possible.