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

_demo/cppintf/foo/bar/bar.cpp

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#define interface struct
+
+interface ICallback {
+	virtual int valA() = 0;
+	virtual double valB() = 0;
+};
+
+extern "C" void f(ICallback* cb) {
+	printf("Hello %d, %lf!\n", cb->valA(), cb->valB());
+}