compiler: better error messages for missing interface method

For golang/go#10700

Change-Id: I1d7232f7f5beb0da55515c9d14c6077ee79c8378
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/273886
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
1 file changed