MDEV-26855: Enable spinning for log_sys_mutex and log_flush_order_mutex

As part of MDEV-26779 we first discovered the effect of enabling spinning for
some critical mutex. MDEV-26779 tried enabling it for lock_sys.wait_mutex and
observed a good gain in performance.

In yet another discussion, Mark Callaghan pointed a reference to pthread based
mutex spin using PTHREAD_MUTEX_ADAPTIVE_NP (MDEV-26769 Intel RTM).

Given the strong references, Marko Makela as part of his comment in #1923
pointed an idea to enable spinning for other mutexes. Based on perf profiling
we decided to explore spinning for log_sys_mutex and log_flush_order_mutex as
they are occupying the top slots in the contented mutex list.

The evaluation showed promising results for ARM64 but not for x86.
So a patch is here-by proposed to enable the spinning of the mutex for
ARM64-based platform.

Author: mysqlonarm

storage/innobase/log/log0log.cc

@@ -175,8 +175,14 @@ void log_t::create()
   ut_ad(!is_initialised());
   m_initialised= true;
 
+#if defined(__aarch64__)
+  mysql_mutex_init(log_sys_mutex_key, &mutex, MY_MUTEX_INIT_FAST);
+  mysql_mutex_init(
+    log_flush_order_mutex_key, &flush_order_mutex, MY_MUTEX_INIT_FAST);
+#else
   mysql_mutex_init(log_sys_mutex_key, &mutex, nullptr);
   mysql_mutex_init(log_flush_order_mutex_key, &flush_order_mutex, nullptr);
+#endif
 
   /* Start the lsn from one log block from zero: this way every
   log record has a non-zero start lsn, a fact which we will use */