[Bug tree-optimization/120979] Missed strdup to malloc + memcpy for known strings

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120979

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note xstrdup  is not the same as strdup ...

```
char *a()
{
  return __builtin_strdump ("aaaa");
}
```

Would need to be changed into:
```
char *a()
{
  const char tt[] = "aaaa";
  char *t = __builtin_malloc(sizeof(tt));
  if (t) __builtin_memcpy(t,tt, sizeof(tt));
  return t;
}
```

I am not 100% sure if it is worth it either.