[Bug tree-optimization/121815] memcmp should expand inline when the len is [0,1]

[kaelfandrew at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121815

--- Comment #1 from Kael Franco <kaelfandrew at gmail dot com> ---
Reduced C testcase:

```
int
src (const char* str, unsigned len)
{
  return __builtin_memcmp("a", str, len != 0);
}
```

Optimized function should return 0 if len == 0,
then return .SPACESHIP ('a', str[0], -1)