pointer-analysis: use new symbolt constructors

To the extent possible, apply resource-acquisition-is-initialisation.
The constructors ensure that at least the most essential fields (name,
type, mode) are set.

Author: tautschnig

src/pointer-analysis/add_failed_symbols.cpp

@@ -36,14 +36,13 @@ void add_failed_symbol(symbolt &symbol, symbol_table_baset &symbol_table)
 {
   if(symbol.type.id()==ID_pointer)
   {
-    symbolt new_symbol;
+    symbolt new_symbol{
+      failed_symbol_id(symbol.name),
+      to_pointer_type(symbol.type).base_type(),
+      symbol.mode};
     new_symbol.is_lvalue=true;
     new_symbol.module=symbol.module;
-    new_symbol.mode=symbol.mode;
     new_symbol.base_name=failed_symbol_id(symbol.base_name);
-    new_symbol.name=failed_symbol_id(symbol.name);
-    new_symbol.type = to_pointer_type(symbol.type).base_type();
-    new_symbol.value.make_nil();
     new_symbol.type.set(ID_C_is_failed_symbol, true);
 
     symbol.type.set(ID_C_failed_symbol, new_symbol.name);