cmd/dist: don't use "uname -v" to recognize GOHOSTARCH

We can use processor architecture or hardware platform as part of
hostname and it leads to misconfiguration of GOHOSARCH.

For example,

$ uname -m -v
FreeBSD 10.1-RELEASE-p5 #0: Tue Jan 27 08:52:50 UTC 2015 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC i386

Change-Id: I499efd98338beff6a27c03f03273331ecb6fd698
Reviewed-on: https://go-review.googlesource.com/4944Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/dist/util.go

@@ -376,7 +376,7 @@ func main() {
 
 	if gohostarch == "" {
 		// Default Unix system.
-		out := run("", CheckExit, "uname", "-m", "-v")
+		out := run("", CheckExit, "uname", "-m")
 		switch {
 		case strings.Contains(out, "x86_64"), strings.Contains(out, "amd64"):
 			gohostarch = "amd64"
@@ -389,7 +389,7 @@ func main() {
 		case strings.Contains(out, "ppc64"):
 			gohostarch = "ppc64"
 		case gohostos == "darwin":
-			if strings.Contains(out, "RELEASE_ARM_") {
+			if strings.Contains(run("", CheckExit, "uname", "-v"), "RELEASE_ARM_") {
 				gohostarch = "arm"
 			}
 		default: