cmd/release: include the ARM version in the arch identifier

Change-Id: I8744e9dd027da390f55e7d75de2d845b83b73b7f
Reviewed-on: https://go-review.googlesource.com/18021
Reviewed-by: Dave Cheney <dave@cheney.net>

cmd/release/release.go

@@ -132,6 +132,9 @@ func (b *Build) String() string {
 	if b.Source {
 		return "src"
 	}
+	if b.Goarm != 0 {
+		return fmt.Sprintf("%v-%v%v", b.OS, b.Arch, b.Goarm)
+	}
 	return fmt.Sprintf("%v-%v", b.OS, b.Arch)
 }