CBMC does not sufficiently validate `__CPROVER_allocated_memory`

[thomasspriggs]

Because __CPROVER_allocated_memory is currently flow insensitive, multiple instances of this intrinsic for the same hardware style memory address should be considered invalid input to cbmc, because that is introducing conflicting specifications of how much memory is allocated. cbmc should check for and reject this type of input.

Additional kinds of checks on this intrinsic/allocation which we should add in order to help ensure our model of hardware memory allocation is sound -

• Checks on duplicate/overlapping allocation definitions for the same address.
• Checks that allocated address and the size of the allocation are constants.
• Potentially, a "reasonable" limit on the maximum size of an allocation.

[feliperodri]

@diffblue/diffblue-opensource