go/gcimporter15: backport of https://golang.org/cl/23012/

Fixes golang/go#16365.

Change-Id: I8e33fbd9f1bf1b4b5d85a5c972ad43414cea57cb
Reviewed-on: https://go-review.googlesource.com/24973
Reviewed-by: Alan Donovan <adonovan@google.com>
4 files changed