Support OpenSSL 1.1.0 in 9.4 branch.

Support OpenSSL 1.1.0 in 9.4 branch.

This commit back-patches the equivalent of the 9.5-branch commits
e2838c580 and 48e5ba61e, so that we can work with OpenSSL 1.1.0 in 9.4.

(Going further back would be a good thing but will take more work;
meanwhile let's see what the buildfarm makes of this.)

Original patches by Andreas Karlsson and Heikki Linnakangas,
back-patching work by Andreas Karlsson.

Patch: https://postgr.es/m/0c817abb-3f7d-20fb-583a-58f7593a0bea@proxel.se
Discussion: https://postgr.es/m/5129.1492293840@sss.pgh.pa.us