Use an OrderedSet for accumulating license files

setuptools/command/sdist.py

@@ -5,7 +5,7 @@ import sys
 import io
 import contextlib
 
-from setuptools.extern import six
+from setuptools.extern import six, ordered_set
 
 from .py36compat import sdist_add_defaults
 
@@ -204,7 +204,7 @@ class sdist(sdist_add_defaults, orig.sdist):
         valid paths to 'self.filelist'.
         """
 
-        files = set()
+        files = ordered_set.OrderedSet()
 
         opts = self.distribution.get_option_dict('metadata')
 

setuptools/dist.py

@@ -409,7 +409,7 @@ class Distribution(_Distribution):
         'long_description_content_type': None,
         'project_urls': dict,
         'provides_extras': ordered_set.OrderedSet,
-        'license_files': list,
+        'license_files': ordered_set.OrderedSet,
     }
 
     _patched_dist = None