[Bug tree-optimization/79349] unused std::string is not optimized away in presence of a call

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79349

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is interesting adding `-D_GLIBCXX_ASSERTIONS` actually GCC then can
optimize away the std::string.