add Makefile targets for fix-whitespace

[geekosaur]

make whitespace now runs fix-whitespace --check --verbose and make fix-whitespace runs fix-whitespace --verbose. You will need to install fix-whitespace yourself, but that's just a cabal install away.

This is another step in the direction of fixing #10263.

Template B: This PR does not modify behaviour or interface

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Include the following checklist in your PR:

• Patches conform to the coding conventions.
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