fix: firtool lowering options CLI flag

[edwardcwang]

As of firtool 1.62.0 the format is --lowering-options=...

Type of Improvement

Documentation or website-related

Desired Merge Strategy

Squash

Release Notes

Reviewer Checklist (only modified by reviewer)

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• Did you do one of the following when ready to merge:
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[seldridge]

This is fine to do, though unnecessary.

LLVM tools will accept either version. I.e., -lowering-options or --lowering-options are the same. The help text, however, always shows a -- for the options.