Errors building //bazel/example/p4:program with Bazel

[qobilidop]

To reproduce:

1. Remove bazel/example from .bazelignore.
2. Run bazel build //bazel/example/p4:program.

I got the following errors:

ERROR: .../external/bazel_tools/platforms/BUILD:14:6: in alias rule @bazel_tools//platforms:x86_32: Constraints from @bazel_tools//platforms have been removed. Please use constraints from @platforms repository embedded in Bazel, or preferably declare dependency on https://github.com/bazelbuild/platforms. See https://github.com/bazelbuild/bazel/issues/8622 for details.
ERROR: .../external/bazel_tools/platforms/BUILD:14:6: Analysis of target '@bazel_tools//platforms:x86_32' failed
ERROR: /path/to/p4c/bazel/example/p4/BUILD.bazel:3:11: While resolving toolchains for target //bazel/example/p4:program: invalid registered toolchain '@go_sdk//:go_linux_386': 
ERROR: Analysis of target '//bazel/example/p4:program' failed; build aborted: 
INFO: Elapsed time: 6.426s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (35 packages loaded, 129 targets configured)

[apinski-cavium]

#3791 (comment)