cmd/dist: run msan test only in testsanitizer on arm64

With latest gcc (7.3.0), misc/cgo/testsanitizer test will fail with reporting sigmentation
fault when running tsan test. On arm64, tsan is not supported currently and only msan test
can be run. So skip tsan test on arm64.

What needs to be pointed out is that msan test can be really run when setting clang
as c/c++ complier.

Fixes #25601

Change-Id: I6ab1a8d9edd243e2ee00ee40bc0abd6a0e6a125c
Reviewed-on: https://go-review.googlesource.com/114857Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testsanitizers/tsan_test.go

@@ -7,9 +7,13 @@ package sanitizers_test
 import (
 	"strings"
 	"testing"
+	"runtime"
 )
 
 func TestTSAN(t *testing.T) {
+	if runtime.GOARCH == "arm64" {
+		t.Skip("skipping test; see https://golang.org/issue/25682")
+	}
 	t.Parallel()
 	requireOvercommit(t)
 	config := configure("thread")