bazelrc line with missing command should fail fast instead of silently ignoring

[alexeagle]

Description of the bug:

It's very easy to forget the command in a bazelrc file, for example this mistake in https://github.com/aspect-build/rules_js/pull/34/files --host_jvm_args=-DBAZEL_TRACK_SOURCE_DIRECTORIES=1 simply has no effect because it's missing a command before the flags appear on that line, the correct way is

startup --host_jvm_args=-DBAZEL_TRACK_SOURCE_DIRECTORIES=1

This silent failure is confusing to users, and a source of bugs. I've seen many cases at clients where lines in the bazelrc are being silently ignored.

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

No response

Which operating system are you running Bazel on?

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What is the output of bazel info release?

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If bazel info release returns development version or (@non-git), tell us how you built Bazel.

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What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

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Have you found anything relevant by searching the web?

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

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