Make order of processing the builtins SCC predictable (#12431)

Various things can go wrong if the order of modules in the builtins
SCC that also includes typing, _typeshed and others is adjusted.

Hopefully fixes #12422. May also fix #12421.

mypy/build.py

@@ -2959,12 +2959,16 @@ def process_graph(graph: Graph, manager: BuildManager) -> None:
         # Order the SCC's nodes using a heuristic.
         # Note that ascc is a set, and scc is a list.
         scc = order_ascc(graph, ascc)
-        # If builtins is in the list, move it last.  (This is a bit of
-        # a hack, but it's necessary because the builtins module is
-        # part of a small cycle involving at least {builtins, abc,
-        # typing}.  Of these, builtins must be processed last or else
-        # some builtin objects will be incompletely processed.)
+        # Make the order of the SCC that includes 'builtins' and 'typing',
+        # among other things, predictable. Various things may  break if
+        # the order changes.
         if 'builtins' in ascc:
+            scc = sorted(scc, reverse=True)
+            # If builtins is in the list, move it last.  (This is a bit of
+            # a hack, but it's necessary because the builtins module is
+            # part of a small cycle involving at least {builtins, abc,
+            # typing}.  Of these, builtins must be processed last or else
+            # some builtin objects will be incompletely processed.)
             scc.remove('builtins')
             scc.append('builtins')
         if manager.options.verbosity >= 2: