Auto merge of #5944 - dwijnand:fix-force-rebuild, r=alexcrichton
Force `cargo fix` to rebuild
Fixes #5736
This is a resubmit of @killercup's #5750, rebased on current master.
@alexcrichton From browsing the code I feel like `-p` would still restrict the packages to rebuild, despite the rebuild flag added. But I might be misreading or not-fully-reading the code. Could you give me some mentoring instructions for the test cases you're concerned with?