cmd/release: don't ship race detector *.syso for other platforms
cmd/release: don't ship race detector *.syso for other platforms

Saves about 800k compressed, 2.2MB on disk.

Updates golang/go#27151

Change-Id: Ie78e02c3956b81c18643c80620f97612d55fdd23
Reviewed-on: https://go-review.googlesource.com/c/144281
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

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