cmd/release: clean $GOROOT/pkg/GOOS_GOARCH_{dynlink,shared,testcshared_shared}
cmd/release: clean $GOROOT/pkg/GOOS_GOARCH_{dynlink,shared,testcshared_shared}

Fixes golang/go#30028

Change-Id: Ie4afee88c43beb92bd7538edfb0f8f2882d67819
Reviewed-on: https://go-review.googlesource.com/c/160660
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/build,golang/build,golang/build,golang/build