Add some tests that make the compiler panick.

examples/tests/c/lib/main.ak

@@ -0,0 +1,14 @@
+pub fn foldr(xs: List(a), f: fn(a, b) -> b, zero: b) -> b {
+  when xs is {
+    [] -> zero
+    [x, ..rest] -> f(x, foldr(rest, f, zero))
+  }
+}
+
+pub fn concat(left: List(a), right: List(a)) -> List(a) {
+  foldr(left, fn(x, xs) { [x, ..xs] }, right)
+}
+
+test concat_1() {
+  concat([1, 2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]
+}