Issue #21629: Merge from 3.4.

diff --cc Misc/NEWS
index 59a07f3bb0a2071f4a0090c24dc5843a3f54f322,4dbcc8c5aeebb3687df166fc82134a12b291c0b3..ad2106a24ad1e57568f9aa45047257c8045bb4d5
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -623,6 -476,6 +623,8 @@@ Test
  Tools/Demos
  -----------
  
++- Issue #21629: Fix Argument Clinic's "--converters" feature.
++
  - Add support for ``yield from`` to 2to3.
  
  - Add support for the PEP 465 matrix multiplication operator to 2to3.