Support for overflow_result-+

[rafaelsamenezes]

Apparently CBMC has a custom handler and structures to deal with overflows.

foo = checked_add(a, b) => foo = overflow_result-+(a,b)

overflow_result: {
  result: int,
  overflow: bool
}

Current solution for ESBMC: esbmc/esbmc@7867f5e

[tautschnig]

In case this helps: diffblue/cbmc#6903 is the PR where we introduced this feature in CBMC (includes a link to the issue explaining why we wanted this in the first place).