Post-push fix for MDEV-11947 InnoDB purge workers fail to shut down

Use the ib_int64_t type alias instead of the standard type int64_t,
so that the code will compile on Microsoft Visual Studio 2013.

storage/innobase/srv/srv0srv.cc

@@ -841,7 +841,7 @@ srv_suspend_thread(
 @return	whether the wait timed out */
 static
 bool
-srv_resume_thread(srv_slot_t* slot, int64_t sig_count = 0, bool wait = true,
+srv_resume_thread(srv_slot_t* slot, ib_int64_t sig_count = 0, bool wait = true,
 		  ulint timeout_usec = 0)
 {
 	bool	timeout;

storage/xtradb/srv/srv0srv.cc

@@ -991,7 +991,7 @@ srv_suspend_thread(
 @return	whether the wait timed out */
 static
 bool
-srv_resume_thread(srv_slot_t* slot, int64_t sig_count = 0, bool wait = true,
+srv_resume_thread(srv_slot_t* slot, ib_int64_t sig_count = 0, bool wait = true,
 		  ulint timeout_usec = 0)
 {
 	bool	timeout;