Fix Unix build breaks in CastableObject
Fix Unix build breaks in CastableObject

yizhang82/corert,tijoytom/corert,krytarowski/corert,shrah/corert,krytarowski/corert,gregkalapos/corert,gregkalapos/corert,krytarowski/corert,sandreenko/corert,krytarowski/corert,gregkalapos/corert,botaberg/corert,shrah/corert,tijoytom/corert,botaberg/corert,yizhang82/corert,tijoytom/corert,gregkalapos/corert,botaberg/corert,botaberg/corert,shrah/corert,tijoytom/corert,yizhang82/corert,sandreenko/corert,sandreenko/corert,yizhang82/corert,shrah/corert,sandreenko/corert