bpo-41369: Finish updating the vendored libmpdec to version 2.5.1

[pitrou]

The vendored libmpdec has been partially updated in 9b9f158, this completes the update to upstream version 2.5.1.

Patch provided by Stefan Krah.

https://bugs.python.org/issue41369

[pitrou]

I've submitted a build on the buildbots here: https://buildbot.python.org/all/#/changes/3354

[rhettinger]

I haven't reviewed this in-detail, but this all looks reasonable after a ten-minute review. Unless someone has objections, it should be applied

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot PPC64LE RHEL8 LTO + PGO 3.x has failed when building commit 73b20ae.

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/458/builds/1279) and take a look at the build logs.
4. Check if the failure is related to this commit (73b20ae) 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/458/builds/1279

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

== Tests result: ENV CHANGED ==

412 tests OK.

10 slowest tests:

• test_concurrent_futures: 2 min 42 sec
• test_multiprocessing_spawn: 1 min 11 sec
• test_multiprocessing_forkserver: 1 min
• test_tokenize: 55.2 sec
• test_multiprocessing_fork: 53.3 sec
• test_asyncio: 52.1 sec
• test_signal: 47.5 sec
• test_unparse: 42.4 sec
• test_io: 39.4 sec
• test_lib2to3: 38.7 sec

1 test altered the execution environment:
test_asyncio

14 tests skipped:
test_devpoll test_gdb test_ioctl test_kqueue test_msilib
test_ossaudiodev test_startfile test_tix test_tk test_ttk_guionly
test_winconsoleio test_winreg test_winsound test_zipfile64

Total duration: 3 min 11 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/sslproto.py", line 321, in __del__
    self.close()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/sslproto.py", line 316, in close
    self._ssl_protocol._start_shutdown()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/sslproto.py", line 590, in _start_shutdown
    self._abort()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/sslproto.py", line 731, in _abort
    self._transport.abort()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/selector_events.py", line 680, in abort
    self._force_close(None)
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/selector_events.py", line 731, in _force_close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/base_events.py", line 745, in call_soon
    self._check_closed()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-ppc64le.lto-pgo/build/Lib/asyncio/base_events.py", line 510, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed