Update to CBMC 5.9

[FrNecas]

Related: https://github.com/peterschrammel/cbmc/pull/23

Changes:

• domains must now implement is_bottom and is_top methods
• ID_malloc deprecated
• some changes to exprt constructors
• union_fidn can no longer be inherited from, fixed by using it as an attribute
• CBMC_VERSION is now passed to CBMC during compilation which seems to make it impossible to mention it in the help message
• GOTO program reading simplification
• Constant propagation now works as expected (except for one test where it produces a wrong result) so I decided to re-enable it

Also memsafety tests which are correct are broken (one of the assertions failed). We tried to investigate the problem with @viktormalik and it seems to be related to changes in CBMC free implementation. Fixing this may be difficult so we agreed that it may be a good idea to leave it for a stable version (once the rebase is finished).

[peterschrammel]

Please update the submodule pointer and merge.