Turn value_address and set_value_address functions into methods

This changes the value_address and set_value_address functions to be
methods of value.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdb/compile/compile-cplus-symbols.c

@@ -156,7 +156,7 @@ convert_one_symbol (compile_cplus_instance *instance,
 		     sym.symbol->print_name ());
 
 	    kind = GCC_CP_SYMBOL_VARIABLE;
-	    addr = value_address (val);
+	    addr = val->address ();
 	  }
 	  break;