[kernel] fix printing of empty initializers for empty unions

src/kernel_services/ast_printing/cil_printer.ml

@@ -911,7 +911,7 @@ class cil_printer () = object (self)
         | _ -> Kernel.fatal "Trying to print malformed initializer"
       in
       if not (Cil.isArrayType t) then
-        Pretty_utils.pp_list ~pre:"{@[<hv>" ~sep:",@ " ~suf:"@]}"
+        Pretty_utils.pp_list ~pre:"{@[<hv>" ~sep:",@ " ~suf:"@]}" ~empty:"{}"
           designated_init fmt initl
       else begin
         let print_index prev_index (designator,init as di) =

tests/syntax/empty_union.i

 /* run.config*
-   STDOPT: +"-machdep gcc_x86_32"
+   STDOPT: +"-machdep gcc_x86_32 -print -ocode @PTEST_NAME@_reparse.c -then @PTEST_NAME@_reparse.c -ocode=''"
  EXIT: 1
    STDOPT:
  */

tests/syntax/oracle/empty_union.0.res.oracle

 [kernel] Parsing empty_union.i (no preprocessing)
+[kernel] Parsing empty_union_reparse.c (with preprocessing)
 /* Generated by Frama-C */
 union empty {
    
 };
-union empty eu = ;
+union empty eu = {};