Remove unused flag that broke clang 3.x.
Remove unused flag that broke clang 3.x.

Fixes #5.

alecthomas/entityx,jaynus/entityx,arvidsson/entityx,alecthomas/entityx,arvidsson/entityx,asmodehn/entityx,jarrettchisholm/entityx,jarrettchisholm/entityx,drewet/entityx,Bablawn3d5/entityx,drewet/entityx,jaynus/entityx,alecthomas/entityx,jaynus/entityx,jarrettchisholm/entityx,Bablawn3d5/entityx,asmodehn/entityx,asmodehn/entityx,arvidsson/entityx,asmodehn/entityx,drewet/entityx,Bablawn3d5/entityx