cmd/go: silence ar with D flag failures

The first call of ar must not show its output in order to avoid useless
error messages about D flag.
The corresponding Go toolchain patch is CL 182077.

Change-Id: I3ac2c60909a95124adf6106c1246b5034918703d
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/183817
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed