libstdc++: [_GLIBCXX_INLINE_VERSION] Adapt dg error messages

libstdc++-v3/ChangeLog

         * testsuite/20_util/bind/ref_neg.cc: Adapt dg-prune-output message.
         * testsuite/20_util/function/cons/70692.cc: Adapt dg-error message.

Ok to commit ?

François