Spurious pointer overflow check failure

[danpoe]

#include <stdlib.h>

void main()
{
  char *p = (char *)10;
  p -= 1;
  p += 1;
  p += -1; // spurious pointer overflow report
  p -= -1; // spurious pointer overflow report
}

CBMC version: 7e27cb2
Operating system: Ubuntu 16.04
Exact command line resulting in the issue: cbmc --pointer-overflow-check test.c
What behaviour did you expect: verification successful
What happened instead: spurious pointer overflow check failures

Regression test PR: #5283