Add new tests for macro nesting

tests/tests2/64_macro_nesting.c

@@ -0,0 +1,10 @@
+#define CAT2(a,b) a##b
+#define CAT(a,b) CAT2(a,b)
+#define AB(x) CAT(x,y)
+
+int main(void)
+{
+  int xy = 42;
+  printf("%d\n", CAT(A,B)(x));
+  return 0;
+}