This makes it easy to configure a thread with various parameters.  The first
is the existing stack_info parameter.

The apic needs to be programmed on each cpu that is brought up.

We used cpu_arch::init_on_cpu() instead of the arch-indepdendent version.

Maintain the list of active timers per-cpu, instead of globally.

This removes the need for locking (other than disabling preemption).

The clock_event interface is awkward in that the callback is global, not
per-cpu.  This requires us to have a global dispatch object that then
uses cpu::current() to pick up the current cpu and dispatch the event.  We
should probably make clock_event explicitly per-cpu in the future.

This ones handles the current working directory in relative pathnames,
and supports the POSIX.1-2008 case where the resolved_path argument is
passed a NULL and then allocated by realpath internally.

Since timers are per-cpu constructs, we need to migrate them when a thread
migrate.  To do that, we need to keep a list of a thread's active timers.

If a timer is expired already, don't remove it from lists.

No functional changes - prepare for making timer lists cpu local.

Each cpu has its own event timer; we rely on this.  Document the requirement.

Also remove other timers that expired simultaneously.

remote wakeups

current_pthread was somehow not thread-local, so pthread_self() returned
the last thread to initialize itself.  The bug manifested itself with
a jvm thread querying its own stack, finding another thread's stack instead,
and reaching the conclusion that it was in a stack overflow, and throwing
an exception.

Fix by making current_pthread thread local.

Each cpu has a queue (actually an array of queues, one for each "waking" cpu)
of threads that are to be woken.  A thread can be queued locklessly, so a
runqueue lock is not needed.

As we don't IPI yet, the queues are polled at strategic points.

While generally useful, it helps now to avoid wakeups to threads that are
no longer there.

* 'master' of github.com:cloudius-systems/osv:
  stop adding libm.so.6 from glibc to bootfs
  warn when we can't load ELF libraries from DT_NEEDED
  warn on unknown ELF section types
  fix up library pathnames in the ELF loader
  fix sem_wait
  add a __fprintf_chk implementation
  add popen/pclose stubs

Now that we actually look for DT_NEEDED libraries in the right place we
fail loading it because we don't support STT_GNU_IFUNC symbols.  But
by now we already have a feature complete libm implementation in our
tree so we don't actually need it anymore.

We want to look for /usr/lib/libfoo instead of /usr/liblibfoo

We need to use a spinlock to protect the semaphore waiting list as
the wakeups can deadlock otherwise.

Also make sure to only wait when we actually have to.

Found during python bringup.