bazel: resolve benchmark deps for downstream bzlmod consumers

[Copilot]

Envoy’s benchmark macros were resolving @benchmark inside Envoy’s repo mapping, which breaks for downstream bzlmod consumers because google_benchmark remains a dev_dependency and is absent when Envoy is not the root module. This change keeps the dependency dev-only in Envoy, adds an external regression target, and shifts benchmark resolution to the caller’s module mapping.

• Why this change

  • Downstream modules using envoy_cc_benchmark_binary could not build benchmarks unless Envoy promoted google_benchmark to a non-dev dep.
  • We do not want that; downstreams that build benchmarks should declare google_benchmark themselves.

• External regression coverage

  • Added a minimal benchmark under bazel/tests/external/ that consumes Envoy as an external module.
  • Declared google_benchmark in the external test module and added the new benchmark target to the external CI build path.
  • This provides a concrete yardstick for the downstream bzlmod use case reported in build: remove dev_dependency = true from google_benchmark #47497.

• Benchmark target split

  • Split //test/benchmark:main into:
    • main_lib: Envoy-owned support deps only
    • main: the in-tree benchmark target that still links @benchmark and @tclap
  • Exported main.cc so the benchmark main can be compiled from the caller context.

• Macro behavior change

  • Reworked envoy_cc_benchmark_binary and envoy_cc_benchmark_dyn_module_binary to:
    • remove the misleading repository parameter
    • add a srcs parameter and append Label("//test/benchmark:main.cc")
    • depend on Label("//test/benchmark:main_lib")
    • pass @benchmark and @tclap as plain string labels so they resolve in the caller’s repo mapping
  • Added small deduping logic so existing in-tree benchmark targets that already list @benchmark do not pick it up twice.

• Downstream contract

  • Documented that downstream bzlmod users of envoy_cc_benchmark_binary must declare:

    bazel_dep(name = "google_benchmark", version = "1.9.5", repo_name = "benchmark")

• Example

  envoy_cc_benchmark_binary(
      name = "benchmark_test",
      srcs = ["benchmark_test.cc"],
  )

  with the downstream module declaring:

  bazel_dep(name = "google_benchmark", version = "1.9.5", repo_name = "benchmark")

[repokitteh-read-only]

As a reminder, PRs marked as draft will not be automatically assigned reviewers,
or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

🐱

Caused by: #47553 was opened by Copilot.

see: more, trace.