compiler: connect the concrete type and the placeholder for circular types
Previously, when creating the backend representation of a
circular type, we resolve the placeholder to a
circular_pointer_type. The backend doesn't know what the
concrete type is.
This CL changes it to resolve the placeholder to the concrete
type instead, so the backend may have better knowledge of the
concrete type.
Reviewed-on: https://go-review.googlesource.com/123738
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@262830 138bc75d-0d04-0410-961f-82ee72b054a4