Require OpenSSL 1.1.x series 1.1.0g or greater

Previous versions have a bug with EVP_CipherInit() when passed a
NULL EVP_CIPHER, per https://github.com/openssl/openssl/pull/4613

ok dtucker@

configure.ac

@@ -2616,6 +2616,10 @@ if test "x$openssl" = "xyes" ; then
 				AC_MSG_ERROR([OpenSSL >= 1.0.1 required (have "$ssl_library_ver")])
 		                ;;
 			100*)   ;; # 1.0.x
+			101000[0123456]*)
+				# https://github.com/openssl/openssl/pull/4613
+				AC_MSG_ERROR([OpenSSL 1.1.x versions prior to 1.1.0g have a bug that breaks their use with OpenSSH (have "$ssl_library_ver")])
+				;;
 			101*)   ;; # 1.1.x
 			200*)   ;; # LibreSSL
 		        *)