Build fail on memcached

it fails on ubuntu with another error

. -I./include -I./libevent -fvisibility=hidden -pthread -I./engines/default_engine -I./include -I./libevent -fvisibility=hidden -pthread -g -O2 -Wall -Werror -pedantic -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -MT default_engine_la-default_engine.lo -MD -MP -MF .deps/default_engine_la-default_engine.Tpo -c -o default_engine_la-default_engine.lo `test -f 'engines/default_engine/default_engine.c' || echo './'`engines/default_engine/default_engine.c
libtool: compile: gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I./include -I./libevent -fvisibility=hidden -pthread -I./engines/default_engine -I./include -I./libevent -fvisibility=hidden -pthread -g -O2 -Wall -Werror -pedantic -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -MT default_engine_la-default_engine.lo -MD -MP -MF .deps/default_engine_la-default_engine.Tpo -c engines/default_engine/default_engine.c -fPIC -DPIC -o .libs/default_engine_la-default_engine.o
engines/default_engine/default_engine.c: In function 'initalize_configuration':
engines/default_engine/default_engine.c:506:22: error: variable 'ret' set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors
make[2]: *** [default_engine_la-default_engine.lo] Error 1