WtFindMysql fixed to work with MySQL & MariaDB

In: wt/cmake/WtFindMysql.txt

Before: SET(MYSQL_LIBRARY "mariadb;mariadbclient" CACHE STRING "Library that provides MySQL/MariaDB API (set to mysqlclient for mysql on unix; libmysql on windows)")

Error in CMake:
** Wt::Dbo: not building MySQL backend.
    Indicate the location of your mariadb or mysqlclient installation using 
    -DMYSQL_PREFIX=... and the library to search for (e.g. mariadb or 
    mysqlclient) using -DMYSQL_LIBRARY=...


Afer: SET(MYSQL_LIBRARY mysqlclient mariadb mariadbclient CACHE STRING "Library that provides MySQL/MariaDB API (set to mysqlclient for mysql on unix; libmysql on windows)")

CMake OK:
** Wt::Dbo: building MySQL backend.