Add a couple more tests for chained #define directives.

One with the chained defines in the opposite order, and one with the
potential to trigger an infinite-loop bug through mutual
recursion. Each of these tests pass already.

tests/003-define-chain-reverse.c

@@ -0,0 +1,3 @@
+#define bar foo
+#define foo 1
+bar

tests/004-define-recursive.c

@@ -0,0 +1,6 @@
+#define foo bar
+#define bar baz
+#define baz foo
+foo
+bar
+baz