MDEV-26467: Actually use spinloop on block_lock

In commit 277ba134
we accidentally omitted this.

storage/innobase/include/srw_lock.h

@@ -151,7 +151,7 @@ class ssux_lock_impl final
   void wr_unlock();
 #else
   /** mutex for synchronization; held by U or X lock holders */
-  srw_mutex writer;
+  srw_mutex_impl<spinloop> writer;
   /** S or U holders, and WRITER flag for X holder or waiter */
   std::atomic<uint32_t> readers;
   /** indicates an X request; readers=WRITER indicates granted X lock */

storage/innobase/sync/srw_lock.cc

@@ -417,7 +417,23 @@ void ssux_lock_impl<spinloop>::wr_wait(uint32_t lk)
   DBUG_ASSERT(writer.is_locked());
   DBUG_ASSERT(lk);
   DBUG_ASSERT(lk < WRITER);
+
+  if (spinloop)
+  {
+    const unsigned delay= srw_pause_delay();
+
+    for (auto spin= srv_n_spin_wait_rounds; spin; spin--)
+    {
+      srw_pause(delay);
+      lk= readers.load(std::memory_order_acquire);
+      if (lk == WRITER)
+        return;
+      DBUG_ASSERT(lk > WRITER);
+    }
+  }
+
   lk|= WRITER;
+
   do
   {
     DBUG_ASSERT(lk > WRITER);