Add work-around for missing client links

Author: lcawl

shared/attributes.asciidoc

@@ -551,3 +551,22 @@ Legacy definitions
 :apm-overview-ref-m:   https://www.elastic.co/guide/en/apm/get-started/master
 :infra-guide:          https://www.elastic.co/guide/en/infrastructure/guide/{branch}
 :a-data-source:        a data view
+
+//////////
+8.x links
+The if directives below are required for 8.x docs that are not yet available.
+Without these if directives, the links fail and break the build.
+//////////
+
+ifdef::8x-missing-links[]
+:enterprise-search-python-ref: https://www.elastic.co/guide/en/enterprise-search-clients/python/master
+:es-dotnet-client:             https://www.elastic.co/guide/en/elasticsearch/client/net-api/master
+:es-php-client:                https://www.elastic.co/guide/en/elasticsearch/client/php-api/master
+:jsclient:                     https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/master
+:es-python-client:             https://www.elastic.co/guide/en/elasticsearch/client/python-api/master
+:es-ruby-client:               https://www.elastic.co/guide/en/elasticsearch/client/ruby-api/master
+:enterprise-search-node-ref:   https://www.elastic.co/guide/en/enterprise-search-clients/enterprise-search-node/master
+:enterprise-search-php-ref:    https://www.elastic.co/guide/en/enterprise-search-clients/php/master
+:enterprise-search-python-ref: https://www.elastic.co/guide/en/enterprise-search-clients/python/master
+:enterprise-search-ruby-ref:   https://www.elastic.co/guide/en/enterprise-search-clients/ruby/master
+endif::[]

shared/versions/stack/8.x.asciidoc

@@ -72,3 +72,8 @@ Synthetics
 API URLs
 ////
 :api-kibana:           https://www.elastic.co/docs/api/doc/kibana/v8
+
+//////////
+8x-missing-links can be: true | false
+//////////
+:8x-missing-links:    true