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

[redi at gcc dot gnu.org]

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

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 35708
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35708&action=edit
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This fixes this specific testcase, but not all cases (if you compare
error_condition objects created in different translation unit compiled with
different GCC versions then whether it works depends on which error_condition
is on the left-hand side).