bpo-40334: Fix broken mkdir -p call in regen-pegen

[gvanrossum]

This caused problems on platforms (like macOS) where MKDIR_P is set to ./install-sh -c -d.

https://bugs.python.org/issue40334

[lysnikolaou]

Yup.

[bedevere-bot]

@gvanrossum: Please replace # with GH- in the commit message next time. Thanks!

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Ubuntu Shared 3.x has failed when building commit 3e89251.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/101/builds/787) and take a look at the build logs.
4. Check if the failure is related to this commit (3e89251) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/101/builds/787

Failed tests:

• test_concurrent_futures

Failed subtests:

• test_shutdown_no_wait - test.test_concurrent_futures.ProcessPoolSpawnProcessPoolShutdownTest

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

405 tests OK.

10 slowest tests:

• test_multiprocessing_spawn: 4 min 57 sec
• test_concurrent_futures: 4 min 38 sec
• test_gdb: 3 min 31 sec
• test_unparse: 3 min 20 sec
• test_tokenize: 2 min 55 sec
• test_capi: 2 min 48 sec
• test_lib2to3: 2 min 34 sec
• test_peg_generator: 2 min 30 sec
• test_multiprocessing_forkserver: 2 min 17 sec
• test_asyncio: 2 min 3 sec

1 test failed:
test_concurrent_futures

17 tests skipped:
test_devpoll test_idle test_ioctl test_kqueue test_msilib
test_ossaudiodev test_startfile test_tcl test_tix test_tk
test_ttk_guionly test_ttk_textonly test_turtle test_winconsoleio
test_winreg test_winsound test_zipfile64

1 re-run test:
test_concurrent_futures

Total duration: 36 min 25 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_concurrent_futures.py", line 542, in test_shutdown_no_wait
    executor.shutdown(wait=False)
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/concurrent/futures/process.py", line 724, in shutdown
    self._executor_manager_thread_wakeup.wakeup()
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/concurrent/futures/process.py", line 80, in wakeup
    self._writer.send_bytes(b"")
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/multiprocessing/connection.py", line 205, in send_bytes
    self._send_bytes(m[offset:offset + size])
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/multiprocessing/connection.py", line 416, in _send_bytes
    self._send(header + buf)
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/multiprocessing/connection.py", line 373, in _send
    n = write(self._handle, buf)
OSError: [Errno 9] Bad file descriptor