Report most cppcheck errors

Summary: If we are going to run it, we might as well get the most bang for the buck.

Test Plan:

arc lint --everything

cppcheck raises a handful of error still. They look legitimate.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6866