Fix for bug #21476: stack overflow crashes server; error-message stack reservation too small

Increase STACK_BUFF_ALLOC to avoid execution_constants test failure on the hpita2.


sql/mysql_priv.h:
  Fix for bug #21476: stack overflow crashes server; error-message stack reservation too small
    - due to the failing execution_constants test on the hpita2, 
      increase STACK_BUFF_ALLOC, that is used in the Item_func::fix_fields() to 
      allocate on the stack a "dummy" buffer large enough for the corresponding exec.

sql/mysql_priv.h

@@ -179,7 +179,7 @@ MY_LOCALE *my_locale_by_number(uint number);
 #define STACK_MIN_SIZE          12000   // Abort if less stack during eval.
 
 #define STACK_MIN_SIZE_FOR_OPEN 1024*80
-#define STACK_BUFF_ALLOC	256	// For stack overrun checks
+#define STACK_BUFF_ALLOC        352     // For stack overrun checks
 #ifndef MYSQLD_NET_RETRY_COUNT
 #define MYSQLD_NET_RETRY_COUNT  10	// Abort read after this many int.
 #endif