By spec, the "long double" in _PyGC_Head requires the union to always be 16-byte
aligned. However, obmalloc only yields 8-byte alignment. Compilers including GCC
8 are starting to use alignment information to do store-merging. So, the "long
double" needs to be changed to a simple "double" as was long ago done in Python
3 by e348c8d154cf6342c79d627ebfe89dfe9de23817. For 2.7, we need to add some
dummy padding to make sure _PyGC_Head stays the same size.

closes https://github.com/python/cpython/pull/6474

(cherry picked from commit 76215a4481191b648de522a4e2120f60822f6b9c)

Co-authored-by: Ned Deily <nad@python.org>

These include:

- bpo-32726: Provide an additional, more modern macOS installer variant that
  supports macOS 10.9+ systems in 64-bit mode only. Upgrade the supplied
  third-party libraries to OpenSSL 1.0.2n and SQLite 3.22.0. The 10.9+
  installer now supplies its own private copy of Tcl/Tk 8.6.8.

- bpo-24414: Default macOS deployment target is now set by ``configure`` to
  the build system's OS version (as is done by Python 3), not ``10.4``;
  override with, for example, ``./configure MACOSX_DEPLOYMENT_TARGET=10.4``.

- bpo-19019: All 2.7 macOS installer variants now supply their own version
  of ``OpenSSL 1.0.2``; the Apple-supplied SSL libraries and root
  certificates are not longer used.  The ``Installer Certificate`` command
  in ``/Applications/Python 2.7`` may be used to download and install a
  default set of root certificates from the third-party ``certifi`` package.

- bpo-11485: python.org macOS Pythons no longer supply a default SDK value
  (e.g. ``-isysroot /``) or specific compiler version default (e.g.
  ``gcc-4.2``) when building extension modules.  Use ``CC``, ``SDKROOT``,
  and ``DEVELOPER_DIR`` environment variables to override compilers or to
  use an SDK.  See Apple's ``xcrun`` man page for more info.

- prepare for pending Apple removal of 32-bit support in future macOS release

Based on patch by Oleg Krasnikov.
(cherry picked from commit c93938b5beea4c3f592119ebee6d4029558db8de)