Add deprecation warning when variable optimizer_search_depth is given
the value 63.
      
  mysql-test/r/greedy_optimizer.result
    Updated with warning text.
  mysql-test/r/mysqld--help-notwin.result
    Updated with warning from mysqld --help --verbose.
  mysql-test/r/mysqld--help-win.result
    Updated with warning from mysqld --help --verbose.
  sql/sys_vars.cc
    Added an update check function to the constructor invocation for
    the optimizer_search_depth variable. The function emits a
    warning message for the value 63.