Light cleanup of the kevent backend.

Some functionality requires particular preprocessor feature flags to be
set but errors are raised if they aren't, so the remedy is to put these
behind relevant feature flags.
  * dispatch_kevent_t has a qos field only when DISPATCH_USE_KEVENT_QOS
  * _dispatch_kq_unote_update requires DISPATCH_HAVE_DIRECT_KNOTES as it
    is only called from functions behind this
  * _dispatch_workloop_actions and the associated enum are only used when
    DISPATCH_USE_KEVENT_WORKLOOP.

Some unused variable void casts are removed (guard_ptr and pp), which do
not refer to variables -- these may be upstream merge artefacts.

A type cast is made to match types for _dispatch_bug_kevent_client. This
function is incorrectly placed behind HAVE_MACH in src/init.c, but to
keep the scope and impact of this commit narrow, we will defer that
change.

Since EVFILT_FS is not supported on all kevent implementations, put these
behind an #ifdef. EVFILT_USER also requires similar handling, but since
EVFILT_USER kevents are used intrinsically as part of the functionality,
these will be handled in a separate commit.

Author: 3405691582

Diff for: src/event/event_kevent.c

@@ -101,7 +101,9 @@ _evfiltstr(short filt)
 	_evfilt2(EVFILT_MACHPORT);
 	_evfilt2(DISPATCH_EVFILT_MACH_NOTIFICATION);
 #endif
+#ifdef EVFILT_FS
 	_evfilt2(EVFILT_FS);
+#endif
 	_evfilt2(EVFILT_USER);
 #ifdef EVFILT_SOCK
 	_evfilt2(EVFILT_SOCK);
@@ -388,16 +390,18 @@ _dispatch_kevent_print_error(dispatch_kevent_t ke)
 	switch (ke->data) {
 	case 0:
 		return;
+#if DISPATCH_USE_KEVENT_QOS
 	case ERANGE: /* A broken QoS was passed to kevent_id() */
 		DISPATCH_INTERNAL_CRASH(ke->qos, "Invalid kevent priority");
+#endif
 	default:
 		// log the unexpected error
 		_dispatch_bug_kevent_client("kevent", _evfiltstr(ke->filter),
 				!ke->udata ? NULL :
 				ke->flags & EV_DELETE ? "delete" :
 				ke->flags & EV_ADD ? "add" :
 				ke->flags & EV_ENABLE ? "enable" : "monitor",
-				(int)ke->data, ke->ident, ke->udata, du);
+				(int)ke->data, ke->ident, (uint64_t)ke->udata, du);
 	}
 }
 
@@ -591,7 +595,6 @@ _dispatch_kq_create(intptr_t *fd_ptr)
 	guardid_t guard = (uintptr_t)fd_ptr;
 	kqfd = guarded_kqueue_np(&guard, GUARD_CLOSE | GUARD_DUP);
 #else
-	(void)guard_ptr;
 	kqfd = kqueue();
 #endif
 	if (kqfd == -1) {
@@ -860,7 +863,6 @@ _dispatch_kq_unote_set_kevent(dispatch_unote_t _du, dispatch_kevent_t dk,
 				du->du_priority),
 #endif
 	};
-	(void)pp; // if DISPATCH_USE_KEVENT_QOS == 0
 }
 
 DISPATCH_ALWAYS_INLINE
@@ -985,6 +987,7 @@ _dispatch_sync_ipc_handoff_end(dispatch_wlh_t wlh, mach_port_t port)
 }
 #endif
 
+#if DISPATCH_HAVE_DIRECT_KNOTES
 DISPATCH_NOINLINE
 static bool
 _dispatch_kq_unote_update(dispatch_wlh_t wlh, dispatch_unote_t _du,
@@ -1055,6 +1058,7 @@ _dispatch_kq_unote_update(dispatch_wlh_t wlh, dispatch_unote_t _du,
 	dispatch_assume_zero(r);
 	return true;
 }
+#endif
 
 #pragma mark dispatch_muxnote_t
 
@@ -1283,6 +1287,7 @@ _dispatch_unote_unregister_direct(dispatch_unote_t du, uint32_t flags)
 #pragma mark -
 #pragma mark dispatch_event_loop
 
+#if DISPATCH_USE_KEVENT_WORKLOOP
 enum {
 	DISPATCH_WORKLOOP_ASYNC,
 	DISPATCH_WORKLOOP_ASYNC_FROM_SYNC,
@@ -1316,6 +1321,7 @@ static char const * const _dispatch_workloop_actions[] = {
 	[DISPATCH_WORKLOOP_SYNC_WAKE]                   = "sync-wake",
 	[DISPATCH_WORKLOOP_SYNC_END]                    = "sync-end",
 };
+#endif
 
 void
 _dispatch_event_loop_atfork_child(void)
@@ -2445,6 +2451,7 @@ const dispatch_source_type_s _dispatch_source_type_vnode = {
 	.dst_merge_evt  = _dispatch_source_merge_evt,
 };
 
+#ifdef EVFILT_FS
 const dispatch_source_type_s _dispatch_source_type_vfs = {
 	.dst_kind       = "vfs",
 	.dst_filter     = EVFILT_FS,
@@ -2477,6 +2484,7 @@ const dispatch_source_type_s _dispatch_source_type_vfs = {
 	.dst_create     = _dispatch_unote_create_without_handle,
 	.dst_merge_evt  = _dispatch_source_merge_evt,
 };
+#endif
 
 #ifdef EVFILT_SOCK
 const dispatch_source_type_s _dispatch_source_type_sock = {