Deprecation warning for ATOMIC_VAR_INIT in mimalloc

[cdce8p]

Bug report

Bug description:

ATOMIC_VAR_INIT is marked as deprecated in C17 and C++20.

/.../cpython/Include/internal/mimalloc/mimalloc/atomic.h:42:14: error: macro 'ATOMIC_VAR_INIT' has been marked as deprecated [-Werror,-Wdeprecated-pragma] (diff)
  #if !defined(ATOMIC_VAR_INIT) || (__STDC_VERSION__ >= 201710L) // c17, see issue #735
  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include/stdatomic.h:54:41: note: macro marked 'deprecated' here
  #pragma clang deprecated(ATOMIC_VAR_INIT)

This was fixed upstream but isn't included in the vendored copy.
microsoft/mimalloc@36ee5f9
microsoft/mimalloc@1325ee6
microsoft/mimalloc#735

CPython versions tested on:

3.13, CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-121487: Fix deprecation warning for ATOMIC_VAR_INIT in mimalloc #121488
• [3.13] gh-121487: Fix deprecation warning for ATOMIC_VAR_INIT in mimalloc (gh-121488) #121504