Change OS X installer builds targeted for 10.10 and above to build

and link with a private copy of OpenSSL, like installers targeted
for 10.5 already do, since Apple has deprecated use of the system
OpenSSL and removed its header files from the Xcode 7 SDK.  Note
that this configuration is not currently used to build any
python.org-supplied installers and that the private copy of
OpenSSL requires its own root certificates.