The bug itself was solved in 3.12 by the addition of __gnu_cxx::__freeres
in the libstdc++ and have valgrind calling it before exit.
However, depending on the version of the libstdc++, the test leak_cpp_interior
was giving different results.
This commit adds some filtering specific to the test, so as to not depend
anymore of the absolute number of bytes leaked, and adds a suppression entry to
ignore the memory allocated by libstdc++.
This allows to have only 2 .exp files, instead of 4 (or worse, if
we would have to handle yet other .exp files depending on the libstdc++
version).
