This change modifies go to create iOS arm64 binaries that pass iTunes
upload validation. Tested with xcode 9.0.1 macOS 10.13.

Fixes #22402.

Change-Id: I3f14c6ac85065e2da88d06edc8682947f6f1cd47
Reviewed-on: https://go-review.googlesource.com/72730Reviewed-by: David Crawshaw <crawshaw@golang.org>