libstdc++: [_GLIBCXX_INLINE_VERSION] Fix test dg-prune-output

     libstdc++-v3/ChangeLog:

             * 
testsuite/20_util/is_complete_or_unbounded/memoization_neg.cc: Adapt 
dg-prune-output to
             _GLIBCXX_INLINE_VERSION mode.


With this patch all tests are Ok in _GLIBCXX_INLINE_VERSION mode (at the 
time I'm writing this).

Ok to commit ?

François