Implement runtime functions for reflect

The reflect package isn't supported yet. But at least the Go
parser/typechecker can now deal with it.

src/runtime/stack.go

@@ -0,0 +1,16 @@
+package runtime
+
+type Func struct {
+}
+
+func FuncForPC(pc uintptr) *Func {
+	return nil
+}
+
+func (f *Func) Name() string {
+	return ""
+}
+
+func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
+	return 0, "", 0, false
+}