bpo-32726: macOS installer and framework enhancements and changes for 3.7.0 (GH-5448)

bpo-32726: macOS installer and framework enhancements and changes for 3.7.0 (GH-5448)

This issue covers various changes for the macOS installers provided via python.org for 3.7.0.

- Provide a provisional new installer variant for macOS 10.9 and later systems with 64-bit (x86_64) architecture only.  Apple has made it known that future versions of macOS will only fully support 64-bit executables and some other third-party software suppliers have chosen 10.9 as their oldest supported system.

- Support **Tcl/Tk 8.6** with the 10.9 installer variant.

- Upgrade **OpenSSL** to 1.1.0g and **SQLite** to 3.22.0.

- The compiler name used for the interpreter build and for modules built with **Distutils / pip** is now _gcc_ rather than _gcc-4.2_. And extension module builds will no longer try to force use of an old SDK if present.