Update to CBMC 5.8

[FrNecas]

I will merge this PR similarly to the last one, this time in 3 commits - all the necessary fixes, commit https://github.com/diffblue/2ls/pull/149/commits/770d34969edf8d7f4dc7079096b7c7151c3637e6 (so that we can easily revert it once propagation is fixed) and commit updating version.

Related: https://github.com/peterschrammel/cbmc/pull/22

Changes

• minor renaming, some deprecations
• a lot of enums transformed into enum classes
• message_handler must not be NULL when get_message_handler is called, otherwise the program exits (fixed in https://github.com/diffblue/2ls/pull/149/commits/17d70420e448c399feaf207421cb961402d1f754)
• assertions generated by CBMC now have the form FALSE || <assertion>, this required fixes in https://github.com/diffblue/2ls/pull/149/commits/a0f6f5f2b51b345ecfb357b39f8564b393377b51 to make memsafety work.
• Messages from CBMC now contain typedefs instead of the typedef-ed structure, fixed this in test https://github.com/diffblue/2ls/pull/149/commits/2b4b91b13a198ddd1aa3427555ae775988e043ff
• Constant propagation is broken in CBMC 5.8, a lot of tests would be failing. So the best temporary solution turned out to be disabling constant propagation by default.

[FrNecas]

Fixed, rebased and squashed, should be ready for merging.