compiler: don't set btype_ too early for alias type

CL 123362 introduced a bug in creating alias type's backend
representation. A type's btype_ should not be set before
named types are converted if it is a placeholder. For alias
type, it is set too early. This may result in unresolved
placeholders. This CL fixes it.

Change-Id: Icf85677c2f25160423f6bf0dfbb9e49b1a322233
Reviewed-on: https://go-review.googlesource.com/123975
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed