valgrind: add support for glibc 2.17 and 2.18

Fixes: http://autobuild.buildroot.net/results/f086e65aca220bc9a5869f8fc8c1dca4d87ada7d/



Signed-off-by: Phil Eichinger <phil@zankapfel.net>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>