[2.7] Backport macOS universal build and installer fixes from 3.6. (GH-6469)

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

Author: ned-deily

Mac/BuildScript/README.txt

@@ -1,7 +1,15 @@
 Building a Python Mac OS X distribution
 =======================================
 
-The ``build-install.py`` script creates Python distributions, including
+WARNING
+-------
+
+The instructions in this README are incomplete and not up-to-date.
+In particular, they do not explain how to create a modern flat installer
+package from the now obsolete bundle-format installer package produced
+by ``build-installer.py``.
+
+The ``build-installer.py`` script creates Python distributions, including
 certain third-party libraries as necessary.  It builds a complete 
 framework-based Python out-of-tree, installs it in a funny place with 
 $DESTROOT, massages that installation to remove .pyc files and such, creates 

Mac/BuildScript/build-installer.py

@@ -0,0 +1,20 @@
+{\rtf1\ansi\ansicpg1252\cocoartf1561\cocoasubrtf200
+{\fonttbl\f0\fswiss\fcharset0 Helvetica;\f1\fnil\fcharset0 LucidaGrande-Bold;\f2\fnil\fcharset0 LucidaGrande;
+\f3\fnil\fcharset0 Monaco;}
+{\colortbl;\red255\green255\blue255;}
+{\*\expandedcolortbl;;}
+\margl1440\margr1440\vieww10540\viewh8400\viewkind0
+\pard\tx720\tx1440\tx2160\tx2880\tx3600\tx4320\tx5040\tx5760\tx6480\tx7200\tx7920\tx8640\pardirnatural\partightenfactor0
+
+\f0\fs28 \cf0 Congratulations!
+\fs24   
+\f1\b\fs28 Python $FULL_VERSION for macOS $MACOSX_DEPLOYMENT_TARGET
+\f2\b0  was successfully installed.
+\fs24 \
+\
+One more thing: to verify the identity of secure network connections, this Python needs a set of SSL root certificates.  You can download and install a current curated set from {\field{\*\fldinst{HYPERLINK "https://pypi.org/project/certifi/"}}{\fldrslt the Certifi project}} by double-clicking on the 
+\f3 Install Certificates
+\f2  icon in {\field{\*\fldinst{HYPERLINK "file://localhost/Applications/Python%20$VERSION/"}}{\fldrslt the Finder window}}.  See {\field{\*\fldinst{HYPERLINK "file://localhost/Applications/Python%20$VERSION/ReadMe.rtf"}}{\fldrslt the 
+\f3 ReadMe
+\f2  file}} for more information.\
+}