[Bug tree-optimization/86955] strlen of a known string in member array plus offset not folded

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86955

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is not folded either:
```
void f4 (struct A* p)
{
  __builtin_strcpy (p->a+1, "123");

  if (__builtin_strlen (p->a + 2) != 2)   // not folded
    __builtin_abort ();
}
```