Ooops ... add required configure support.
The previous commit assumed we have a configure probe for
SSL_CTX_set_cert_cb. v15 lacks that, so add it now.
(Details borrowed from
36f40ce2d.)
Reported-by: Thomas Munro <thomas.munro@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CA+hUKG+fLqyweHqFSBcErueUVT0vDuSNWui-ySz3+d_APmq7dw@mail.gmail.com
Backpatch-through: 15 only