/usr/include/GNUstep/ is in sogo 2.2.17a-1.1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/GNUstep/GDLContentStore/
/usr/include/GNUstep/GDLContentStore/EOAdaptorChannel+GCS.h
/usr/include/GNUstep/GDLContentStore/GCSAlarmsFolder.h
/usr/include/GNUstep/GDLContentStore/GCSChannelManager.h
/usr/include/GNUstep/GDLContentStore/GCSContext.h
/usr/include/GNUstep/GDLContentStore/GCSFieldInfo.h
/usr/include/GNUstep/GDLContentStore/GCSFolder.h
/usr/include/GNUstep/GDLContentStore/GCSFolderManager.h
/usr/include/GNUstep/GDLContentStore/GCSFolderType.h
/usr/include/GNUstep/GDLContentStore/GCSSessionsFolder.h
/usr/include/GNUstep/GDLContentStore/GCSSpecialQueries.h
/usr/include/GNUstep/GDLContentStore/GCSStringFormatter.h
/usr/include/GNUstep/GDLContentStore/NSURL+GCS.h
/usr/include/GNUstep/NGCards/
/usr/include/GNUstep/NGCards/CardElement.h
/usr/include/GNUstep/NGCards/CardGroup.h
/usr/include/GNUstep/NGCards/CardVersitRenderer.h
/usr/include/GNUstep/NGCards/NGCards.h
/usr/include/GNUstep/NGCards/NGVCard.h
/usr/include/GNUstep/NGCards/NGVCardPhoto.h
/usr/include/GNUstep/NGCards/NGVCardReference.h
/usr/include/GNUstep/NGCards/NGVList.h
/usr/include/GNUstep/NGCards/NSArray+NGCards.h
/usr/include/GNUstep/NGCards/NSCalendarDate+ICal.h
/usr/include/GNUstep/NGCards/NSCalendarDate+NGCards.h
/usr/include/GNUstep/NGCards/NSDictionary+NGCards.h
/usr/include/GNUstep/NGCards/NSString+NGCards.h
/usr/include/GNUstep/NGCards/iCalAlarm.h
/usr/include/GNUstep/NGCards/iCalAttachment.h
/usr/include/GNUstep/NGCards/iCalByDayMask.h
/usr/include/GNUstep/NGCards/iCalCalendar.h
/usr/include/GNUstep/NGCards/iCalDataSource.h
/usr/include/GNUstep/NGCards/iCalDateTime.h
/usr/include/GNUstep/NGCards/iCalEntityObject.h
/usr/include/GNUstep/NGCards/iCalEvent.h
/usr/include/GNUstep/NGCards/iCalEventChanges.h
/usr/include/GNUstep/NGCards/iCalFreeBusy.h
/usr/include/GNUstep/NGCards/iCalJournal.h
/usr/include/GNUstep/NGCards/iCalObject.h
/usr/include/GNUstep/NGCards/iCalPerson.h
/usr/include/GNUstep/NGCards/iCalRecurrenceCalculator.h
/usr/include/GNUstep/NGCards/iCalRecurrenceRule.h
/usr/include/GNUstep/NGCards/iCalRepeatableEntityObject.h
/usr/include/GNUstep/NGCards/iCalTimeZone.h
/usr/include/GNUstep/NGCards/iCalTimeZonePeriod.h
/usr/include/GNUstep/NGCards/iCalToDo.h
/usr/include/GNUstep/NGCards/iCalTrigger.h
/usr/include/GNUstep/NGCards/iCalUTCOffset.h
/usr/include/GNUstep/NGCards/iCalXMLRenderer.h
/usr/include/GNUstep/SOGo
/usr/include/GNUstep/SOGoUI/
/usr/include/GNUstep/SOGoUI/SOGoAptFormatter.h
/usr/include/GNUstep/SOGoUI/UIxComponent.h
/usr/include/GNUstep/SOGoUI/UIxJSClose.h