Define USE_TLS when compiling libmysql.dll, to avoid crashing when

loaded at runtime.


extra/comp_err.c:
  Don't use DBUG after my_end, crashes on Windows with USE_TLS.
include/my_dbug.h:
  Add missing DBUG_LEAVE in non-debug builds.
include/my_pthread.h:
  Add comment explaining USE_TLS.
libmysql/cmakelists.txt:
  Add USE_TLS to avoid crashing when loading libmysql.dll at runtime.
mysys/cmakelists.txt:
  Add USE_TLS to avoid crashing when loading libmysql.dll at runtime.
mysys/my_init.c:
  Don't use DBUG after my_thread_end(), as it crashes on Windows TLS.

extra/comp_err.c

@@ -188,8 +188,9 @@ int main(int argc, char *argv[])
       DBUG_RETURN(1);
     }
     clean_up(lang_head, error_head);
+    DBUG_LEAVE;			/* Can't use dbug after my_end() */
     my_end(info_flag ? MY_CHECK_ERROR | MY_GIVE_INFO : 0);
-    DBUG_RETURN(0);
+    return 0;
   }
 }