Let ENVIRONMENT take multiple keywords in cmake_parse_arguments
Let ENVIRONMENT take multiple keywords in cmake_parse_arguments

Move from `one_value_keywords` to `multi_value_keywords` arg.

vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa