Support verbose output via --subcommands

It would be nice if the entire configure / make / cmake output would be passed to the standard output when the Bazel `--subcommands` flag is set, to make debugging easier.

Specifically, because sometimes what I'm trying to do is figure out what are the right flags or cache entries for the build to pick up my dependencies, which can be lots of trial-and-error. If it is an optional dependency, the build process would continue, building the entire library without my dependency, and I have to wait it out so that I could look at the build log.

If I could see the output early, I could cancel the build and retry with different flags.

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If there is already some way to do this, maybe I just missed it, it would be nice then to document it somewhere more visible.

No files or tests are named. Start by tracing how Bazel --subcommands reaches the configure, make, and cmake build steps, and check whether their output is captured or suppressed. Done means forwarding that output early when the flag is set, or documenting the existing way to enable it if support already exists.

Written by the indexing model from the issue text.