compiler: avoid knock-on errors from invalid interfaces

The test case for this is issue11614.go.

Change-Id: Id3b44e6ae58cc9fbbfbeaaaecdb7f6c60e964803
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/278192
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2 files changed