gtk: a couple more C cleanups

src/apprt/gtk/App.zig

@@ -1319,10 +1319,10 @@ pub fn run(self: *App) !void {
 
 // This timeout function is started when no surfaces are open. It can be
 // cancelled if a new surface is opened before the timer expires.
-pub fn gtkQuitTimerExpired(ud: ?*anyopaque) callconv(.C) c.gboolean {
+pub fn gtkQuitTimerExpired(ud: ?*anyopaque) callconv(.c) c_int {
     const self: *App = @ptrCast(@alignCast(ud));
     self.quit_timer = .{ .expired = {} };
-    return c.FALSE;
+    return 0;
 }
 
 /// This will get called when there are no more open surfaces.
@@ -1354,7 +1354,7 @@ fn stopQuitTimer(self: *App) void {
         .off => {},
         .expired => self.quit_timer = .{ .off = {} },
         .active => |source| {
-            if (c.g_source_remove(source) == c.FALSE) {
+            if (glib.Source.remove(source) == 0) {
                 log.warn("unable to remove quit timer source={d}", .{source});
             }
             self.quit_timer = .{ .off = {} };