[Bug libstdc++/56166] std::string::clear() can throw despite being marked noexcept

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56166

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. this is fixed when using the new std::__cxx11::basic_string in GCC 5