Allow specifying a target for a given rule

[duarten]

It should be possible to override the current target on a per-rule basis, as some rules compile binaries to run on specific platforms. For example, I want to compile AWS Lambda functions targeting x86_64-unknown-linux-musl on a Mac. The rust_binary adds a --target=x86_64-apple-darwin arg to rustc, which I can't override.

[duarten]

It seems I can't specify target_compatible_with on rust_binary rules, although the Bazel documentation says it should be defined for all build rules.

[UebelAndre]

I believe this is a Bazel 4.0 feature. That documentation isn't in the 3.7 version, only master.

bazelbuild/bazel#12455

[duarten]

Oh :)