Addition to fix for

BUG#25712 - insert delayed and check table run together report
            crashed tables

Let MY_THREADSAFE have distinct value. Some functions call my_seek
passing MyFlags argument directly to it. This may cause unnecessary
locks, which may finally lead to a dead-lock (specifically see my_lock).

include/my_sys.h

@@ -73,8 +73,8 @@ extern int NEAR my_errno;		/* Last error in mysys */
 #define MY_ALLOW_ZERO_PTR 64	/* my_realloc() ; zero ptr -> malloc */
 #define MY_FREE_ON_ERROR 128	/* my_realloc() ; Free old ptr on error */
 #define MY_HOLD_ON_ERROR 256	/* my_realloc() ; Return old ptr on error */
-#define MY_THREADSAFE	128	/* pread/pwrite:  Don't allow interrupts */
 #define MY_DONT_OVERWRITE_FILE 1024	/* my_copy; Don't overwrite file */
+#define MY_THREADSAFE 2048      /* my_seek(): lock fd mutex */
 
 #define MY_CHECK_ERROR	1	/* Params to my_end; Check open-close */
 #define MY_GIVE_INFO	2	/* Give time info about process*/