Added constructor to auxilary symbol instead of a helper function

The auxilary function had the same flags requried for the test, so added
a utility constructor that allows specifying of name and type.

Author: thk123

src/util/symbol.h

@@ -145,6 +145,14 @@ class auxiliary_symbolt:public symbolt
     is_file_local=true;
     is_auxiliary=true;
   }
+
+  auxiliary_symbolt(const irep_idt &name, const typet &type):
+    auxiliary_symbolt()
+  {
+    this->name=name;
+    this->base_name=name;
+    this->type=type;
+  }
 };
 
 /*! \brief Symbol table entry of function parameter