test that hexagon scalar output matches checked-in code

[folkertdev]

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[rustbot]

r? @davidtwco

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• Owners of files modified in this PR: @Amanieu, @adamgemmell, @davidtwco, @folkertdev, @sayantn
• @Amanieu, @adamgemmell, @davidtwco, @folkertdev, @sayantn expanded to Amanieu, adamgemmell, davidtwco, folkertdev, sayantn
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[folkertdev]

cc @androm3da