Optimize InnoDB code around mutexes assuming InnoDB locks are uncontended

The InnoDB engine locks have low contention during OLTP_PS/RO sysbench tests. Assuming this we used compiler specific attributes to annotate code near mutexes making code path acquiring lock easier. Specifically, branches which lead to ut_delay() function were marked `unlikely` and functions which call ut_delay() were marked `cold`. We got persistent +2% improvement in sysbench OLTP_PS 128 thread, meanwhile sysbench OTLP_RO/RW results almost didn't change.

Our environment: Kunpeng 920 (64 cores), Ubuntu 20.04, kernel 5.6.0 with 64K pages, gcc-9.3.0.

Look at the TTASEventMutex implementation, for instance. Here, we can mark while(!try_lock()) as unlikely:

void enter(

		uint32_t	max_spins,

		uint32_t	max_delay,

		const char*	filename,

		uint32_t	line)

		UNIV_NOTHROW

	{

		uint32_t	n_spins = 0;

		uint32_t	n_waits = 0;

		const uint32_t	step = max_spins;

		while (UNIV_UNLIKELY(!try_lock())) {

                ...