internal/runtime/atomic: fix TestAnd64 and TestOr64

The local variable may not be 64bit aligned, which caused arm tests
to fail.

Fixes #67077

Change-Id: Ia3ae4abcc90319cb10cd593bdc7994cc6eeb3a28
Reviewed-on: https://go-review.googlesource.com/c/go/+/581916
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
diff --git a/src/internal/runtime/atomic/atomic_andor_test.go b/src/internal/runtime/atomic/atomic_andor_test.go
index 631a6e6..5b594d8 100644
--- a/src/internal/runtime/atomic/atomic_andor_test.go
+++ b/src/internal/runtime/atomic/atomic_andor_test.go
@@ -54,6 +54,7 @@
 func TestAnd64(t *testing.T) {
 	// Basic sanity check.
 	x := uint64(0xffffffffffffffff)
+	sink = &x
 	for i := uint64(0); i < 64; i++ {
 		old := x
 		v := atomic.And64(&x, ^(1 << i))
@@ -131,6 +132,7 @@
 func TestOr64(t *testing.T) {
 	// Basic sanity check.
 	x := uint64(0)
+	sink = &x
 	for i := uint64(0); i < 64; i++ {
 		old := x
 		v := atomic.Or64(&x, 1<<i)