Item_bool fixed to behave smarter with NOT operation.

MDEV-11039 - Add new scheduling algorithm for reducing tail latencies (for 10.2)

        strings/json_lib.c added as a JSON library.
        SQL frunction added with sql/item_jsonfunc.h/cc

Rebase

Sync upstream and rebase.

On PPC64 high-loaded server may crash due to assertion failure in InnoDB
rwlocks code.

This happened because load order between "recursive" and "writer_thread"
wasn't properly enforced.

Clean-up periodic mutex/rwlock waiters wake up. This was a hack needed to
workaround broken mutexes/rwlocks implementation. We must have sane
implementations now and don't need these anymore: release thread is
guaranteed to wake up waiters.

Removed redundant ifdef that has equivalent code in both branches.

Removed os0atomic.h and os0atomic.ic: not used anymore.

Clean-up unused cmake checks.

No point to issue RELEASE memory barrier in os_thread_create_func(): thread
creation is full memory barrier.

No point to issue os_wmb in rw_lock_set_waiter_flag() and
rw_lock_reset_waiter_flag(): this is deadcode and it is unlikely operational
anyway. If atomic builtins are unavailable - memory barriers are most certainly
unavailable too.

RELEASE memory barrier is definitely abused in buf_pool_withdraw_blocks(): most
probably it was supposed to commit volatile variable update, which is not what
memory barriers actually do. To operate properly it needs corresponding ACQUIRE
barrier without an associated atomic operation anyway.

ACQUIRE memory barrier is definitely abused in log_write_up_to(): most probably
it was supposed to synchronize dirty read of log_sys->write_lsn. To operate
properly it needs corresponding RELEASE barrier without an associated atomic
operation anyway.

Removed a bunch of ACQUIRE memory barriers from InnoDB rwlocks. They're
meaningless without corresponding RELEASE memory barriers.

Valid usage example of memory barriers without an associated atomic operation:
http://en.cppreference.com/w/cpp/atomic/atomic_thread_fence

Replaced InnoDB atomic operations with server atomic operations.

Moved INNODB_RW_LOCKS_USE_ATOMICS - it is always defined (code won't compile
otherwise).

NOTE: InnoDB uses thread identifiers as a target for atomic operations.
Thread identifiers should be considered opaque: any attempt to use a
thread ID other than in pthreads calls is nonportable and can lead to
unspecified results.

Simplified InnoDB mutex implementations, corrected memory barriers usage, use
server atomic builtins.