cl: c.Func (llgo.funcAddr); demo: cppintf (how to use c++ interface)

_demo/cppintf/foo/foo.go

@@ -0,0 +1,22 @@
+package foo
+
+import (
+	"unsafe"
+)
+
+const (
+	LLGoFiles   = "bar/bar.cpp"
+	LLGoPackage = "link"
+)
+
+type Callback struct {
+	Vptr *CallbackVtbl
+}
+
+type CallbackVtbl struct {
+	ValA unsafe.Pointer
+	ValB unsafe.Pointer
+}
+
+//go:linkname F C.f
+func F(cb *Callback)