[CI] Use --all-targets with cargo check

[jswrenn]

Ensures that examples, benchmarks, etc. are also checked.

Fixes #95.

[joshlf]

Thanks! One uber nit, but otherwise looks good.

[joshlf]

Looks like the current errors are probably caused by not passing the right linker as described in rust-lang/rust#28924. It may be worth just punting on this for cargo build and only doing it for cargo check unless there's an easy way to provide the linker flag that doesn't significantly increase the complexity of our CI tests or their configs.

[joshlf]

This is captured by our build matrix.