libstdc++ testsuite make targets check-parallel and check-performance don't work anymore

[Paolo Carlini]

.. and also:

performance/ext/pb_ds/priority_queue_text_pop_mem.cc
.../libstdc++-v3/scripts/check_performance: line 41: 16905 Segmentation 
fault      ./$EXE_NAME &>tmp.$FILE_NAME

Paolo.