fix build on Linux
fix build on Linux

jacobdai/CuraEngine-1,alex1818/CuraEngine,alephobjects/CuraEngine,fxtentacle/CuraEngine,mspark93/CuraEngine,alex1818/CuraEngine,patrick3coffee/CuraTinyG,electrocbd/CuraEngine,foosel/CuraEngine,derekhe/CuraEngine,mspark93/CuraEngine,alex1818/CuraEngine,uus169/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,jacobdai/CuraEngine-1,markwal/CuraEngine,uus169/CuraEngine,fxtentacle/CuraEngine,totalretribution/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,derekhe/CuraEngine,markwal/CuraEngine,uus169/CuraEngine,alephobjects/CuraEngine,electrocbd/CuraEngine,ROBO3D/CuraEngine,mspark93/CuraEngine,pratikshashroff/pcura,fxtentacle/CuraEngine,totalretribution/CuraEngine,markwal/CuraEngine,Ultimaker/CuraEngine,pratikshashroff/pcura,patrick3coffee/CuraTinyG,foosel/CuraEngine,foosel/CuraEngine,pratikshashroff/pcura,ROBO3D/CuraEngine,derekhe/CuraEngine,electrocbd/CuraEngine,jacobdai/CuraEngine-1,patrick3coffee/CuraTinyG