Support cross-compilation for arm64

Instead of requiring builds take place on arm64 hardware, we should try to cross-compile from the current CentOS builder.

There are a few steps needed:
1. Make sure the right tools are in place in the gcr.io/bazel-public/centos7-releaser:latest image
1. Define the `cc_toolchain` entries for the tools, that support cross-compilation
1. Define the `cc_toolchain_suite` (legacy) or `toolchain` and `platform` (new hotness) targets needed to support cross-compilation.
1. This may also mean further changes to bazel to support enabling [`--incompatible_enable_cc_toolchain_resolution`](https://github.com/bazelbuild/bazel/issues/7260) for Bazel itself
1. Update the release scripts to properly use the new config.