Reduce stack size

WSREP_LOG increased the stack size of all function, where it was used,
with 1024 bytes, even if it would never called. What's worse is that one
a Mac with Lion 10.7, the stack size was increased with 1024* number of
calls per function.

By moving WSREP_LOG() to a function, the stack size on Lion in function
mysql_execute() was reduced from 18K to 12K. On my main Linux machine
with gcc 5.4 the reduction was from 5k to 4k.

sql/wsrep_mysqld.cc

@@ -246,6 +246,17 @@ static void wsrep_log_cb(wsrep_log_level_t level, const char *msg) {
   }
 }
 
+void wsrep_log(void (*fun)(const char *, ...), const char *format, ...)
+{
+  va_list args;
+  char msg[1024];
+  va_start(args, format);
+  vsnprintf(msg, sizeof(msg) - 1, format, args);
+  va_end(args);
+  (fun)("WSREP: %s", msg);
+}
+
+
 static void wsrep_log_states (wsrep_log_level_t   const level,
                               const wsrep_uuid_t* const group_uuid,
                               wsrep_seqno_t       const group_seqno,

sql/wsrep_mysqld.h

@@ -192,13 +192,8 @@ extern wsrep_seqno_t wsrep_locked_seqno;
     ? wsrep_forced_binlog_format : (ulong)(my_format))
 
 // prefix all messages with "WSREP"
-#define WSREP_LOG(fun, ...)                                       \
-    do {                                                          \
-        char msg[1024] = {'\0'};                                  \
-        snprintf(msg, sizeof(msg) - 1, ## __VA_ARGS__);           \
-        fun("WSREP: %s", msg);                                    \
-    } while(0)
-
+void wsrep_log(void (*fun)(const char *, ...), const char *format, ...);
+#define WSREP_LOG(fun, ...) wsrep_log(fun,  ## __VA_ARGS__)
 #define WSREP_LOG_CONFLICT_THD(thd, role)                                      \
     WSREP_LOG(sql_print_information, 	                                       \
       "%s: \n "       	                                                       \