I found on mirror 2 packages with different names but that contain the same files (but version is different):
Name xorg-libXScrnSaver Version 1.2.2 Category x-window Description The XScrnSaver Library Website http://www.x.org/ Sizes 16K/32K Depends xorg-libXext
and
Name xorg-libXss Version 1.2.1 Category x-window Description Xorg screen saver module. Website http://www.x.org/ Sizes 16K/32K Depends xorg-libXext
libXss.so.1 is required to run iron-linux with rc3/rolling; xorg-libXScrnSaver should be added to the depends of the package.