compiler: emit type specific functions for aliases

    
    If we have an alias for a struct or array that requires a
    type-specific function, don't emit the function with the alias name.
    Emit it with the struct/array as usual.
    
    Test case is https://golang.org/cl/62531.
    
    Reviewed-on: https://go-review.googlesource.com/62412

From-SVN: r252747