fix cmake build

I'm on ubuntu LTS 14.04 x64. 
I have tried ./build.sh but I got some errors. 
So I've patched your CMakeLists.txt to make it work in my env








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src/haywire/connection_consumer.c:11:9: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
     int rc;
         ^
src/haywire/connection_consumer.c: In function ‘ipc_connect_cb’:
src/haywire/connection_consumer.c:43:9: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
     int rc;
         ^
src/haywire/connection_consumer.c: In function ‘connection_consumer_new_connection’:
src/haywire/connection_consumer.c:58:9: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
     int rc = 0;
         ^
src/haywire/connection_consumer.c: In function ‘get_listen_handle’:
src/haywire/connection_consumer.c:80:9: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
     int rc;