MDEV-8241: Debug build on Windows is broken: error LNK2019: unresolved...

MDEV-8241: Debug build on Windows is broken: error LNK2019: unresolved external symbol pthread_detach referenced in function ma_checkpoint_init

pthread_detach() replaced with pthread_detach_this_thread()

pthread_detach_this_thread() definition fixed

include/my_pthread.h

@@ -182,7 +182,7 @@ int pthread_cancel(pthread_t thread);
 #define pthread_key(T,V) pthread_key_t V
 #define my_pthread_getspecific_ptr(T,V) my_pthread_getspecific(T,(V))
 #define my_pthread_setspecific_ptr(T,V) pthread_setspecific(T,(void*) (V))
-#define pthread_detach_this_thread()
+#define pthread_detach_this_thread() { pthread_t tmp=pthread_self() ; pthread_detach(tmp); }
 #define pthread_handler_t EXTERNC void *
 typedef void *(* pthread_handler)(void *);
 

storage/maria/ma_checkpoint.c

@@ -340,7 +340,6 @@ int ma_checkpoint_init(ulong interval)
     {
       /* thread lives, will have to be killed */
       checkpoint_control.status= THREAD_RUNNING;
-      pthread_detach(th);
     }
   }
   DBUG_RETURN(res);
@@ -574,6 +573,8 @@ pthread_handler_t ma_checkpoint_background(void *arg)
   sleeps= 1;
   pages_to_flush_before_next_checkpoint= 0;
 
+  pthread_detach_this_thread();
+
   for(;;) /* iterations of checkpoints and dirty page flushing */
   {
 #if 0 /* good for testing, to do a lot of checkpoints, finds a lot of bugs */