drd/tests/std_thread2: Make this test independent of the libstdc++ version

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14022 a5019735-40e9-0310-863c-91ae7b9d1cf9
glibc-2.X-drd.supp: Add support for --num-callers=1

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14023 a5019735-40e9-0310-863c-91ae7b9d1cf9