chore: Create Nix-specific .bazelrc.local for libiconv

[indiv0]

Pull Request Description

Rather than applying the extra_exec_rustc_flags to all Bazel builds via MODULE.bazel, apply it via a .bazelrc.local created conditionally on Darwin via flake.nix.

This makes it so that Nix-specific configurations are not present for all users, only for those users that require it.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.
• If meaningful changes were made to logic or tests affecting Enso Cloud integration in the libraries,
  or the Snowflake database integration, a run of the Extra Tests has been scheduled.
  • If applicable, it is suggested to paste a link to a successful run of the Extra Tests.

[Frizi]

Does this conflict with .bazelrc.local created manually? Also, will builds created that way be runnable on bare macos machines?

[indiv0]

Does this conflict with .bazelrc.local created manually? Also, will builds created that way be runnable on bare macos machines?

@Frizi It'll just give you a warning if you already have .bazelrc.local rather than overwrite it.

Yes, builds created that way appear to be runnable on bare macos machines.