All the GNUstep versions I see, including 1.24.9 has the following method signature:

• (NSInteger) secondsFromGMTForDate: (NSDate*)aDate;

It's about this specific method:

2607 @implementation NSCalendarDate (OPENSTEP)
2608
2609 - (NSCalendarDate) dateByAddingYears: (NSInteger)years
2610 months: (NSInteger)months
2611 days: (NSInteger)days
2612 hours: (NSInteger)hours
2613 minutes: (NSInteger)minutes
2614 seconds: (NSInteger)seconds
2615 {
2616 NSCalendarDate c;
2617 NSTimeInterval s;
2618 NSTimeInterval oldOffset;
2619 NSTimeInterval newOffset;
2620 NSInteger i, year, month, day, hour, minute, second, mil;

last line was original (in 1.24.6)
2610 int i, year, month, day, hour, minute, second, mil;

Fixed in 2.3.11 and 3.0.3.