Fix compilation on GCC 5.3.
Fix compilation on GCC 5.3.

OTS reviewed by @vexocide

JackieXie168/rethinkdb,bpradipt/rethinkdb,bpradipt/rethinkdb,JackieXie168/rethinkdb,bpradipt/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,mbroadst/rethinkdb,bpradipt/rethinkdb,catroot/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,bpradipt/rethinkdb,catroot/rethinkdb,bchavez/rethinkdb,catroot/rethinkdb,catroot/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,bpradipt/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,mbroadst/rethinkdb,bpradipt/rethinkdb,mbroadst/rethinkdb,bpradipt/rethinkdb,catroot/rethinkdb,bpradipt/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,catroot/rethinkdb,robertjpayne/rethinkdb,grandquista/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,bchavez/rethinkdb,catroot/rethinkdb,catroot/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,mbroadst/rethinkdb,mbroadst/rethinkdb,JackieXie168/rethinkdb,bchavez/rethinkdb,JackieXie168/rethinkdb,bchavez/rethinkdb,grandquista/rethinkdb,mbroadst/rethinkdb,JackieXie168/rethinkdb,JackieXie168/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,mbroadst/rethinkdb,robertjpayne/rethinkdb,bchavez/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,bchavez/rethinkdb,robertjpayne/rethinkdb,jmptrader/rethinkdb,bchavez/rethinkdb,robertjpayne/rethinkdb