Use bazel starlark flags instead of defines

[steeve]

Inspired by https://github.com/bazelbuild/rules_apple/commit/4287aa277e14c693a9c036a8382521964c6951b3, I figure it'd be worthwhile to track this somewhere.

In the case of this commit, instead of:

--define=apple.package_symbols=yes

It would be, for instance:

--@build_bazel_rules_apple//config:package_symbols=true

rules_go has it now and it's very nice to use: https://github.com/bazelbuild/rules_go/blob/8f4ebbd09b1a82a684f839c3eadddc6db7277c3a/go/modes.rst#building-pure-go-binaries

[thii]

Nice. rules_apple uses a lot of defines at the moment so changing them to Starlark flags might need a migration path. I would wait for the upstream branch to do it.

[steeve]

@thii Oh absolutely, I wasn't trying to point to your commit in particular, it just reminded me that rules_apple would need to migrate sometime, and there wasn't an issue to track that.