compiler: Don't make erroneous type descriptors.

compiler: Don't make erroneous type descriptors.

    There is no need to make type descriptors for named types when there
    are errors during package compilation.  Particularly, if the error in
    package compilation is from a malformed named type, there is no
    guarantee a type descriptor can be created.

    Fixes golang/go#11560.

    Reviewed-on: https://go-review.googlesource.com/12792

From-SVN: r226527