Keep usePlatformsRepoForConstraints value in host cfg

[AlessandroPatti]

The value gets reset to the default (true) so setting --noincompatible_use_platforms_repo_for_constraints has no effect if the target using the constraint is build for the host config.

Related issue: https://github.com/bazelbuild/bazel/issues/8622

[gregestren]

@aranguyen could you review this? I think this makes sense.

[aranguyen]

@AlessandroPatti is this pr still in progress? There seems to be some failures in the presubmit

[AlessandroPatti]

@aranguyen No, it is ready for review. The failure was just a flake, a new run passed.