Dump-C: do not produce c_bit_field declarations

goto-program conversion may introduce temporaries of c_bit_field type.
These, however, are not permitted outside structs in C. Instead, change
their types to plain bitvector types to use `__CPROVER_bitvector[n]`
syntax.

Author: tautschnig

src/goto-instrument/goto_program2code.cpp

@@ -1435,6 +1435,15 @@ void goto_program2codet::cleanup_code(
 
     if(code.op0().type().id()==ID_array)
       cleanup_expr(to_array_type(code.op0().type()).size(), true);
+    else if(code.op0().type().id() == ID_c_bit_field)
+    {
+      c_bit_field_typet original_type = to_c_bit_field_type(code.op0().type());
+      bitvector_typet bv_type =
+        to_bitvector_type(original_type.underlying_type());
+      bv_type.set_width(original_type.get_width());
+      bv_type.remove(ID_C_c_type);
+      code.op0().type() = std::move(bv_type);
+    }
 
     add_local_types(code.op0().type());