Disable the compilation of the built-in _abc module. For example, on Python 3.7 apply the following patch:diff --git a/Modules/Setup.dist b/Modules/Setup.distindex8cc6bf0540..4015527b32 100644--- a/Modules/Setup.dist+++ b/Modules/Setup.dist@@ -114,7 +114,7 @@ _weakref _weakref.c                 # weak references _functools -DPy_BUILD_CORE _functoolsmodule.c   # Tools for working with functions and callable objects _operator _operator.c                  # operator.add() and similar goodies _collections _collectionsmodule.c      # Container types-_abc _abc.c                            # Abstract base classes+#_abc _abc.c                           # Abstract base classes itertools itertoolsmodule.c            # Functions creating iterators for efficient looping atexit atexitmodule.c                  # Register functions to be run at interpreter-shutdown _signal -DPy_BUILD_CORE signalmodule.c@@ -363,7 +363,8 @@ xxsubtype xxsubtype.c # Uncommenting the following line tells makesetup that all following modules # are not built (see above for more detail). #-#*disabled*+*disabled* # #_sqlite3 _tkinter _curses pyexpat #_codecs_jp _codecs_kr _codecs_tw unicodedata+_abcRecompile Python, check:$ ./python -c 'import _abc'ModuleNotFoundError: No module named '_abc'Run:$ ./python -u -m test -R 3:3 test_functools -m test_mro_conflicts Error without _abc:test test_functools crashed -- Traceback (most recent call last):  File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/runtest.py", line 180, in runtest_inner    refleak = dash_R(the_module, test, test_runner, ns.huntrleaks)  File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/refleak.py", line 71, in dash_R    abcs)  File "/home/vstinner/prog/python/3.7/Lib/test/libregrtest/refleak.py", line 148, in dash_R_cleanup    obj.register(ref())  File "/home/vstinner/prog/python/3.7/Lib/_py_abc.py", line 60, in register    raise TypeError("Can only register classes")TypeError: Can only register classesWith built-in _abc module, regrtest is fine.The problem comes from pure-Python reimplementation of abc._get_dump() inLib/test/libregrtest/refleak.py:    def _get_dump(cls):        # For legacy Python version        return (cls._abc_registry, cls._abc_cache,                cls._abc_negative_cache, cls._abc_negative_cache_version)The first item tuple must be a set of weak references. Currently, it's a weak set of strong references.Attached PR fix the issue.

New changeset79b5d29041bd85ea3baa050b3fa2481344ea35c9 by Victor Stinner in branch 'master':bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733)https://github.com/python/cpython/commit/79b5d29041bd85ea3baa050b3fa2481344ea35c9

New changeset2368d86ed1249505b10561e005fc57f4884619c1 by Victor Stinner (Miss Islington (bot)) in branch '3.7':bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733) (GH-12734)https://github.com/python/cpython/commit/2368d86ed1249505b10561e005fc57f4884619c1