[Bug libstdc++/51558] Declaration of unspecialized std::hash<_Tp>::operator()(_Tp) turns compile-time errors into link-time errors

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51558

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-12-15 
02:24:08 UTC ---
Uhmm, I don't know, probably yes. If we are in doubt we can as well use what
I'm going to attach, which resolves the src/ fallback. Which change leads to
the best error messages?