go/internal/gccgoimporter: support for type aliases

This is essentially a copy of the changes in https://golang.org/cl/35268/
but with Go1.9 specific tests factored out into a separate file with build
tag.

For golang/go#18130.

Change-Id: I235693e1bc6145bb53bfd3b343647704c8e82e61
Reviewed-on: https://go-review.googlesource.com/35269
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
3 files changed