Backport of 01ddd608b85c.

zipimport should use the same optimization level as the interpreter.

Issue #28188: Use PyMem_Calloc() to get rid of a type-limits warning and an extra memset() call in _ssl.c.

Issue #28120: Fix dict.pop() for splitted dictionary when trying to remove a
"pending key" (Not yet inserted in split-table).

Patch by Xiang Zhang.

A newer instance of this option, enabled in the configure script when
building outside the source tree, made this redundant.

find_empty_slot() only supports combined dict

Patch by David Dudson.

Patch by Stephen J. Turnbull.

Issue #28105.

is now part of the official flags.