Filter: Implement direct recursion

Direct recursion almost worked, just crashed on function signature check.
Split function parsing such that function signature is saved before
function body is processed. Recursive calls are marked so they can be
avoided during f_same() and similar code walking.

Also, include tower of hanoi solver as a test case.

filter/decl.m4

@@ -376,6 +376,7 @@ case INST_NAME(): {
 #undef whati
 #undef item
   dest->items[pos].fi_code = what->fi_code;
+  dest->items[pos].flags = what->flags;
   dest->items[pos].lineno = what->lineno;
   break;
 }
@@ -647,6 +648,7 @@ FID_WR_PUT(4)m4_dnl
 struct f_inst {
   struct f_inst *next;			/* Next instruction */
   enum f_instruction_code fi_code;	/* Instruction code */
+  enum f_instruction_flags flags;	/* Flags, instruction-specific */
   enum f_type type;			/* Type of returned value, if known */
   int size;				/* How many instructions are underneath */
   int lineno;				/* Line number */