libmemcached: disable sanitizer

The tests are flawed and we don't generally enable a dozen hardening
CFLAGS automatically. Fixes:
http://autobuild.buildroot.net/results/a84/a84ab4f0fdea6bbab971ba379e3066cddb25bfaa/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>