Using bazel-toolchain 5.1.0

I'm trying to upgrade [rules_foreign_cc](https://github.com/bazelbuild/rules_foreign_cc) to use [bazel-toolchain 5.1.0](https://github.com/bazelbuild/bazel-toolchains/releases/tag/v5.1.0) but do not know how to convert `rbe_autoconfig` to the modern equivalent (or what the modern equivalent is). Can someone provide a snippet of what is required?

Start by reviewing how rules_foreign_cc currently references bazel-toolchain 5.1.0 and locate the rbe_autoconfig usage described in the issue. Compare that setup with the modern equivalent and document a working conversion snippet; done means the required configuration is clear enough for a user to follow.

Written by the indexing model from the issue text.