swift234

When unifying two type variables, make sure the new representative type
variable has the must-be-materializable bit set if the old one does.
When assigning a fixed type to a type variable that must be
materializable, transfer the bit to any type variables within the fixed
type, as appropriate.

Add Options field to SavedTypeVariableBinding to save/restore type
variable options during solution.

<rdar://problem/21026806> Propagate MustBeMaterializable bit among type variables appropriately

Swift SVN r28883