Fix fixme in PackedStructs.

Instead of relying testing that the size of pointers is 64bit the
size of registers should be tested. Also it should be a fatal
error to reverse a long long on an architecture that does not
support reverse 64bit read/writes.
Bug 24982

Author: bschommer

cparser/PackedStructs.ml

@@ -36,7 +36,7 @@ let byteswapped_fields : (ident * string, unit) Hashtbl.t
 
 let rec can_byte_swap env ty =
   match unroll env ty with
-  | TInt(ik, _) -> (sizeof_ikind ik <= !config.sizeof_ptr (*FIXME*), sizeof_ikind ik > 1)
+  | TInt(ik, _) -> (sizeof_ikind ik <= !config.sizeof_intreg, sizeof_ikind ik > 1)
   | TEnum(_, _) -> (true, sizeof_ikind enum_ikind > 1)
   | TPtr(_, _) -> (true, true)          (* tolerance? *)
   | TArray(ty_elt, _, _) -> can_byte_swap env ty_elt
@@ -66,7 +66,7 @@ let transf_field_decl mfa swapped loc env struct_id f =
   if swapped then begin
     let (can_swap, must_swap) = can_byte_swap env f.fld_typ in
     if not can_swap then
-      error loc "cannot byte-swap field of type '%a'"
+      fatal_error loc "cannot byte-swap field of type '%a'"
         Cprint.typ f.fld_typ;
     if must_swap then
       Hashtbl.add byteswapped_fields (struct_id, f.fld_name) ()
@@ -141,7 +141,7 @@ let use_reversed = ref false
 let bswap_read loc env lval =
   let ty = lval.etyp in
   let (bsize, aty) = accessor_type loc env ty in
-  assert (bsize = 16 || bsize = 32 || (bsize = 64 && !config.sizeof_ptr = 8));
+  assert (bsize = 16 || bsize = 32 || (bsize = 64 && !config.sizeof_intreg = 8));
   try
     if !use_reversed then begin
       let (id, fty) =
@@ -168,7 +168,7 @@ let bswap_write loc env lhs rhs =
   let ty = lhs.etyp in
   let (bsize, aty) =
     accessor_type loc env ty in
-  assert (bsize = 16 || bsize = 32 || (bsize = 64 && !config.sizeof_ptr = 8));
+  assert (bsize = 16 || bsize = 32 || (bsize = 64 && !config.sizeof_intreg = 8));
   try
     if !use_reversed then begin
       let (id, fty) =