The Microsoft Windows implementations of SRWLOCK and WaitOnAddress()
include some spin loop logic before entering the operating system kernel.
Let us avoid duplicating some of that spin loop logic.

Thanks to Vladislav Vaintroub for this fix.

While waiting for for I/O completion, let us skip spin loops.
Even on fast storage, reading a page into the buffer pool takes
so long that a spin loop would only end up wasting CPU time.

block_lock::s_lock_nospin(): A no-spin variant of acquiring a shared
buffer page latch. Regular s_lock() always involveis a spin loop.

ssux_lock_impl::rd_lock_spin(), ssux_lock_impl::rd_lock_nospin():
Split from rd_wait().

ssux_lock_impl::rd_lock(): Invoke either rd_lock_nospin() or
rd_lock_try() and rd_lock_spin().

buf_page_get_low(): After acquiring a page latch on an io-fixed block,
try to optimize operations on the page latch.

buf_read_page(): Return a pointer to a buffer-fixed, non-read-fixed page,
or nullptr in case of an error.

buf_inc_get(): Wrapper for buf_inc_get(ha_handler_stats*),
to read the thread-local variable mariadb_stats before updating it.

IORequest::read_complete(): Assert that the page is both read-fixed
and buffer-fixed. Sample recv_sys.recovery_on only once.
Buffer-unfix the page when the asynchronous read completes.

buf_page_t::read_complete(): Assert that the page is both
read-fixed and buffer-fixed.

buf_page_t::read_wait(): Wait for a read-fixed and buffer-fixed page
to be only buffer-fixed, by acquiring a shared latch.

buf_page_init_for_read(): Return a pointer to a buffer-fixed block
descriptor pointer, bitwise-ORed with 1 in case the block already
exists in the buffer pool.

buf_read_ahead_update(), buf_read_ahead_update_sql(): Common code
for updating some statistics counters.

buf_read_page_low(): Replace the parameter sync with err, which will
return an error code to a synchronous caller. Add a parameter for
thread-local mariadb_stats.
Return the pointer to the block, or the special values nullptr
(read failure) or -1 or -2 for asynchronous reads.
Increment the statistics when a synchronous read was requested.
In a synchronous read, if the page has already been allocated in
the buffer pool but it is read-fixed, wait for the read to complete.

buf_page_get_zip(): Get a buffer-fixed page from buf_read_page(),
and unfix() it. Our caller is relying solely on a page latch.

buf_read_page_background(): Update the statistics if supplied.

This reverts commit a2614ab.