This adds much of https://golang.org/cl/35731 and
    https://golang.org/cl/35732 to the gofrontend code.
    
    This is a step toward updating libgo to the 1.9 release.  The
    gofrontend already supports type aliases, and this is required for
    correct support of type aliases when used as embedded fields.
    
    The change to expressions.cc is to handle the << 1, used for the
    newly renamed offsetAnon field, in the constant context used for type
    descriptor initialization.
    
    Reviewed-on: https://go-review.googlesource.com/62710

From-SVN: r252746