Description of the problem / feature request:

We use --run_under with collect_coverage to get fuzz-coverage in Envoy:
https://github.com/envoyproxy/envoy/blob/master/.bazelrc#L149

This works perfectly with Bazel 3.6.0 but broken in Bazel 3.7.0

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Checkout https://github.com/envoyproxy/envoy/
Run: ci/run_envoy_docker.sh "ci/do_ci.sh bazel.fuzz_coverage //test/integration:h1_capture_fuzz_test"

What operating system are you running Bazel on?

Ubuntu 18.04

What's the output of bazel info release?

release 3.7.0

Any other information, logs, or outputs that you want to share?

With subcommands, bazel 3.6.0 generates:

external/bazel_tools/tools/test/test-setup.sh external/bazel_tools/tools/test/collect_coverage.sh external/envoy/bazel/coverage/fuzz_coverage_wrapper.sh test/integration/h1_capture_fuzz_test ...

While bazel 3.7.0 generates:

external/bazel_tools/tools/test/test-setup.sh external/bazel_tools/tools/test/collect_coverage.sh envoy/bazel/coverage/fuzz_coverage_wrapper.sh test/integration/h1_capture_fuzz_test ...

Lacking of external/ in the 2nd parameter is why this is broken.

Our failing CI logs can be found at https://dev.azure.com/cncf/envoy/_build/results?buildId=58183&view=logs&j=7b6d60aa-b5de-5f9b-678c-063d31881e76&t=e31ced1d-8def-5d31-02c0-2d875dd6ed2d