[Bug tree-optimization/86611] missing -Warray-bounds on a large negative index into a string in lp64

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86611

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Another test case, except this one triggers a warning in lp64 but not in ilp32,
because of the same folding in fre1:

void f (int);

void g (void)
{
  f (L"123456789"[-__PTRDIFF_MAX__ - 1]); 
}