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 to 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 ARM-based platform.