WSREP() appears on radar in OLTP RO

Data comes from Sandy Bridge system running sysbench OLTP RO in 1 thread against 1 table.

Time to time I can see WSREP() macro taking considerable amount of time. Since it is used quite frequently I'd suggest to optimize it a bit. Original macro is as following:

#define WSREP_ON \

  (global_system_variables.wsrep_on)

#define WSREP(thd) \

  (WSREP_ON && wsrep && (thd && thd->variables.wsrep_on))

• there should be no need to check "thd" - in most (if not all) cases it should be available
• there should be no need to check "wsrep" - make sure it is set inline with wsrep_on
• there should be no need to check "global_system_variables.wsrep_on"

This leaves

#define WSREP(thd) (thd)->variables.wsrep_on