Before this fix, the performance schema was not available
    for embedded builds, in libmysqld.

    This is an issue for SHOW STATUS and SHOW VARIABLES
    statements, which can only be supported with
    show_compatibility_56=on.

    With this fix, the performance_schema is available
    for embedded builds.

    Note that only a subset is supported,
    with no instrumentation collected.

    With this fix,
    - SHOW GLOBAL STATUS
    - SHOW GLOBAL VARIABLES
    - SHOW SESSION STATUS
    - SHOW SESSION VARIABLES
    can now be executed using only the performance_schema tables,
    even in embedded builds.

    This clears the path to remove
    - the corresponding INFORMATION_SCHEMA implementation,
    - the show_compatibility_56 variable itself.