Do not exporting mysqld entry points directly.
This is needed for mariabackup, to load encryption plugins on Windows.
All plugins are "pure" by default. To mark plugin "impure"
it should use RECOMPILE_FOR_EMBEDDED or STORAGE_ENGINE keyword.
Extend existing plugins to support
* SHOW QUERY_RESPONSE_TIME
* FLUSH QUERY_RESPONSE_TIME
* SHOW LOCALE
move userstat tables to use the new API instead of
hand-coded syntax