While it is ok to disregard the error, it would be better to create a unit that would contain the code for your functions. This way the main project file can have a uses statement that will satisfy the IDE. Example:

(* Main project file *)
library Project ;
uses
  Unit ;
exports
  AddLong index   name 'ADDLONG' resident;
begin
end.
(* unit 's code *)
unit Unit ;
interface
function AddLong(a : longint;
                 b : longint) :  longint
{$IFDEF Win32} stdcall; {$ELSE} ; export; {$ENDIF}
implementation
function AddLong(a : longint;
                 b : longint) :  longint;
begin
  AddLong := a + b;
end;
end.