Fix build with clang on travis
Fix build with clang on travis

Possible an old libstdc++ issue? Doesn't seem to repro locally here

steveschnepp/OpenApoc,FranciscoDA/OpenApoc,FranciscoDA/OpenApoc,steveschnepp/OpenApoc,Istrebitel/OpenApoc,Istrebitel/OpenApoc,FranciscoDA/OpenApoc,pmprog/OpenApoc,pmprog/OpenApoc