The origin tagKey is just dirname if no tags input which will cause
pkgCache missmatch if other imported pkg explicit on GOARCH or GOOS

This CL will add GOOS and GOARCH to tagKey

Fixes #8425
Fixes #21181

Change-Id: Ifc189cf6746d753ad7c7e5bb60621297fc0a4e35
Reviewed-on: https://go-review.googlesource.com/c/138315Reviewed-by: Robert Griesemer <gri@golang.org>