C extraction: use partial for C assert

examples/multiprecision/div.mlw

@@ -3970,7 +3970,6 @@ let wmpn_divrem_1 (q x:t) (y:limb) (sz:int32) : limb
               = value q (sx - sy + 1) * value y sy
                 + value r sy }
     ensures { value r sy < value y sy }
-    diverges
   =
     let nx = malloc (UInt32.(+) (UInt32.of_int32 sx) 1) in
     c_assert (is_not_null nx);

stdlib/mach/c.mlw

@@ -192,9 +192,8 @@ module C
     ensures  { forall i. old p2.min <= i < old p2.max ->
                          (pelts p2)[i] = old (pelts p2)[i] }
 
-  val c_assert (e:bool) : unit
+  val partial c_assert (e:bool) : unit
     ensures { e }
-    diverges
 
   (** Printing *)