internal/cabi: check and skip param empty type

internal/cabi/_testdata/wrap/empty.c

@@ -0,0 +1,14 @@
+struct empty {
+};
+
+struct empty demo1(struct empty a) {
+    return a;
+}
+
+int demo2(int v, struct empty a) {
+    return v;
+}
+
+int demo3(int v, struct empty a, int v2) {
+    return v + v2;
+}