Update to CBMC 5.7

[FrNecas]

Following up on https://github.com/peterschrammel/cbmc/pull/21 , adjusting 2LS to the changes in CBMC 5.7. I will squash the commits before this PR is merged to have an atomic compilable commit but leaving it as is (per type of change) to make reviewing easier. May also require changing the CBMC commit used once https://github.com/peterschrammel/cbmc/pull/21 is merged.

Major changes

• abstract domains have to implement make_bottom, make_top and make_entry methods. The changes also required adjusting merge return value in our domains to make the analyses work correctly. The fix was inspired by https://github.com/diffblue/cbmc/pull/327/
• goto_inlinet no longer recomputes locations after inlining, 2LS must call it itself (see https://github.com/diffblue/cbmc/pull/262)
• new types of memsafety asserts lead to the assert numbering in test changing
• otherwise just some minor renaming

[FrNecas]

Proposal for how this should be merged: firstly merge the PR in CBMC, modify https://github.com/diffblue/2ls/pull/148/commits/acbeed7801ebca0f0fcdaa27d54d2b7ec27b21bf so that it points to a correct commit, squash this whole PR into 2 commits - one commit for the changes themselves and one for 2LS version update. Do you agree @peterschrammel or can you think of a better way to handle this?

[peterschrammel]

Proposal for how this should be merged

Yes, please.

[FrNecas]

Rebased onto 2ls-prerequisites-cbmc-5.7, squashed the commits, ready to be merged. Thanks for the quick reviews.