Support passing features to Cargo

[abonander]

I created a bin target for using Honggfuzz with my library (reverted on master because of this issue and also because cargo-fuzz works on WSL now):

• https://github.com/abonander/mvp-tree-rs/blob/c1f57813fe61d2c20845bae92b441a2f64fd8513/Cargo.toml
• https://github.com/abonander/mvp-tree-rs/blob/1734fab76cba614f98ae173453971c736d584e3c/src/bin/honggfuzz_iter.rs

However, I cannot pass the honggfuzz feature to Cargo because the cargo-hfuzz executable doesn't support it.

[abonander]

As a temporary solution I've made honggfuzz non-optional but it's not satisfactory.

[PaulGrandperrin]

Hi @abonander, I'm not a big fan of how features work in cargo because of this exact situation but anyway, there is 2 solutions:

• you can pass the feature argument to cargo build with an env var like this

  HFUZZ_BUILD_ARGS="--features=honggfuzz" cargo hfuzz run honggfuzz_iter

  This is not very nice looking or intuitive but I'm planning to find a better solution in the next major version of the CLI.

• you can make the honggfuzz dependancy conditional on the fuzzing cfg tag like so:

  [target.'cfg(fuzzing)'.dependencies]
  honggfuzz = { version = "0.5"}

Please don't hesitate to reopen if you have any questions or suggestions!