[Bug libstdc++/66438] libstdc++ 5.1 broke binary compat with old code using std::error_category

[costamagnagianfranco at yahoo dot it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66438

--- Comment #4 from Gianfranco <costamagnagianfranco at yahoo dot it> ---
The problem actually is Debian has gcc-4.9 as default compiler, and the
libstdc++ provided in testing is from gcc-5.