Similar to commit f7684f0c (MDEV-26855)
we will try to enable the adaptive spinloop for lock_sys.wait_mutex
on ARMv8.

Enabling any form of spinloop for lock_sys.wait_mutex did not show a
significant improvement in our tests on AMD64.

Spinning can be argued to be a hack to reduce the impact on mutex
contention. It would be better to adjust the code to reduce
contention in the first place.