There is no easy way to understand what user intent was and whether
they wanted to use a dynamic import or not.
If we skip logging such errors, it breaks common use cases such as
https://golang.org/issue/12810.
It's a better approach to expose the underlying mechanism and
be more verbose with the error messages.
Fixes #12810.
Change-Id: I7e922c9e848382690d9d9b006d7046e6cf93223b
Reviewed-on: https://go-review.googlesource.com/15756 Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Andrew Gerrand <adg@golang.org>