Revert "Add new darwin CC toolchain for tests (#3460)"

[linzhp]

This reverts #3460.

What type of PR is this?

Bug fix

What does this PR do? Why is it needed?
Revert cd98170 to unblock rules_go release

Which issues(s) does this PR fix?

Fixes #3498

Other notes for review
@keith FYI

[keith]

if you have only the command line tools you won't be able to run those tests starting with bazel 7.x. So this isn't a long term fix.

[linzhp]

if you have only the command line tools you won't be able to run those tests starting with bazel 7.x

Can you give more context on that? Does it only affect those tests or Go packages in general? //go/tools/releaser is a pretty simple Go package, so I assume if affects all Go packages. It would be a pretty big migration effort to install full XCode on all dev machines in a big corporation.

[linzhp]

Also, we should move towards a direction of hermetic C++ compilers (e.g., using https://github.com/uber/bazel-zig-cc) . Overriding a generic @bazel_tools//tools/cpp:toolchain with a local toolchain further breaks the hermeticity, right?

[keith]

The toolchain you're removing here is only needed for the test that uses an objc_library, so otherwise you should be able to disable it. The problem is the env var isn't enough because of this config:

https://github.com/bazelbuild/rules_go/blob/13aa4706394734625e441c9334d88dc3bd566e40/.bazelrc#L1-L4

so we also need a way to opt out of that in this case 🤔

[linzhp]

We can have a different buildkite step to add those toolchains and run the objc_library.

[keith]

sounds good, note that this change might break rules_go in the bazel downstream pipeline

[linzhp]

Should we add those flags to bazel downstream pipeline too?

[keith]

i think it gets them from your .bazelci config