[Bug tree-optimization/122754] strlen missed opt with vectorization turned on

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122754

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Even the simple:
```
#include <string>

int g(void)
{
  std::string a="a";
  return __builtin_strlen(a.c_str());
}
```
is not optimized to 1 due to this issue.