Sort input files

when building packages (e.g. for openSUSE Linux)
(random) filesystem order of input files
influences ordering of functions in the output,
thus without the patch, builds (in disposable VMs) would usually differ.

See https://reproducible-builds.org/ for why this matters.

Author: bmwiedemann

setup.py

@@ -141,6 +141,7 @@ def restore_cencode():
     else:
         link_flags = ['-fPIC', '-lstdc++']
 
+sources.sort()
 sass_extension = Extension(
     '_sass',
     sources,