[Bug c++/60750] double free after std::move on string inside throw when compiled with optimization

[sshannin at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60750

--- Comment #3 from sshannin at gmail dot com ---
As a note that may help pin things down, removing either call to std::move() or
removing the concatenation with err_prefix done in call to the
std::runtime_error constructor seems to resolve this (or mask it).