Support for OpenSSL 1.1.0:

- symbols get_rfc..._prime_... have been
  renamed to BN_get_rfc..._prime_...

Backport of r1740652 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-openssl-1.1.0-compat@1755865 13f79535-47bb-0310-9956-ffa450edef68