Fix OrderedSet `__repr__` protocol for non-string objects

Prefer using `repr` on the keys to `str` since `repr` is guaranteed to
be implemented, and will return something "good enough"

mesonbuild/mesonlib.py

@@ -708,7 +708,8 @@ class OrderedSet(collections.MutableSet):
     def __repr__(self):
         # Don't print 'OrderedSet("")' for an empty set.
         if self.__container:
-            return 'OrderedSet("{}")'.format('", "'.join(self.__container.keys()))
+            return 'OrderedSet("{}")'.format(
+                '", "'.join(repr(e) for e in self.__container.keys()))
         return 'OrderedSet()'
 
     def add(self, value):