C++ bool is at least one byte wide

[tautschnig]

Do not treat "bool" as a single bit, which is what __CPROVER_bool is for.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[martin-cs]

I'm listed as a reviewer for this but the specific commit that is novel to this branch doesn't seem to touch "my" areas. Am happy to review but I'd suggest we get the supporting things merged first.

[tautschnig]

Adding do-not-merge (to be read as "do not review").

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: fd39953).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/89554493
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.