Fix bug where certain integer constant expressions would have type signed long when they should have type unsigned long.

This affected binary or unary expressions with constant operands, at least one of which was of type unsigned long.

The following test case demonstrates the problem:

#include <stdio.h>
int main (void)
{
        if (0 + 0x80000000ul < 0) puts("error 1");
        if (~0ul < 0) puts("error 2");
}

Expression.pas

@@ -910,11 +910,9 @@ var
          end {else if}
       else if token.kind = longconst then begin
          IntVal := token.lval;
-         ekind := longconst;
          end {else if}
       else begin
          IntVal := token.lval;
-         ekind := longconst;
          unsigned := true;
          end; {else}
       end; {IntVal}