Create FileStream explicitly in CppWriter (#1203)
Create FileStream explicitly in CppWriter (#1203)

`File.Create` will open an overlapped handle which is really
unnecessary.
yizhang82/corert,krytarowski/corert,shrah/corert,sandreenko/corert,tijoytom/corert,shrah/corert,krytarowski/corert,tijoytom/corert,krytarowski/corert,tijoytom/corert,yizhang82/corert,sandreenko/corert,mjp41/corert,sandreenko/corert,tijoytom/corert,gregkalapos/corert,yizhang82/corert,gregkalapos/corert,sandreenko/corert,botaberg/corert,botaberg/corert,shrah/corert,kyulee1/corert,yizhang82/corert,mjp41/corert,krytarowski/corert,kyulee1/corert,mjp41/corert,botaberg/corert,gregkalapos/corert,gregkalapos/corert,mjp41/corert,kyulee1/corert,kyulee1/corert,mjp41/corert,shrah/corert,botaberg/corert