Update glm to 0.9.7.4
Update glm to 0.9.7.4

It seems the old head has been removed from upstream?

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