Make MathF public for corefx facade production
Make MathF public for corefx facade production

[tfs-changeset: 1652774]

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