cmd/align64: test program to force compile failure on GOARCH=386

Demonstrates how to get a 64-bit aligned struct on 32-bit arch. Related to golang/go#63131

Author: ydnar

cmd/align64/main.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+	"sync/atomic"
+	"unsafe"
+)
+
+type S struct {
+	_ [0]atomic.Uint64
+	v uint32
+}
+
+func main() {
+	var v S
+	fmt.Printf("size: %d align: %d", unsafe.Sizeof(v), unsafe.Alignof(v))
+	var i uintptr
+	i = uintptr(unsafe.Alignof(v) << 29)
+	_ = i
+}