cmd/go: clean the directory path containing the packages
The heuristic for determining if the packages or commands are stale
fails as the mtime comparison happens even though the GOROOT and
current package paths are the same, since the path name isn't
canonicalized before the comparison (GOROOT is).
Fixes: #12690
Change-Id: Ia7d142fbbed8aac2bd2f71d1db4efd1f3ff5aece
Reviewed-on: https://go-review.googlesource.com/16483 Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>