CN: add a test for the self-ref init case

Cerberus treats this as UB, whereas some Linux code seems to assume
it works. Add an "unknown" category to the CN tests for code where
it's not clear if it should be rejected or not.

tests/cn/self_ref_init.unknown.c

@@ -0,0 +1,19 @@
+
+/* based on a problematic example from linux kvm/pgtable.c */
+
+struct str {
+  int x;
+  int y;
+};
+
+int f (int x)
+/*@ requires (0 <= x) && (x < 200) @*/
+{
+  struct str str_inst = {
+    .x = x + 2,
+    .y = str_inst.x + 3,
+  };
+
+  return str_inst.y;
+}
+

tests/run-cn.sh

@@ -6,7 +6,7 @@ DIRNAME=$(dirname $0)
 
 set -e
 
-SUCC=$(find $DIRNAME/cn -name '*.c' | grep -v '\.error\.c')
+SUCC=$(find $DIRNAME/cn -name '*.c' | grep -v '\.error\.c' | grep -v '\.unknown\.c')
 
 for TEST in $SUCC
 do