Imported from prex.  Note that the test isn't wired up yet as we'll need
more infrastructure changes to run it.

Don't waste power during idle.

Wastes power.

Instead, spin for a bit looking for work to do, then enter a low-power
state and wait for an interrupt to pull us out of it.

Also add an arch independent name for it.

The whole idea of namespaces is to prevent namespace pollution, using a
"using namespace" in a header negates that.  Remove.

Noticed by Guy.

Add a detached thread class (with a private destructor, so it can only be
allocated on the heap).  The implementation uses a reaper thread to wait
until the detached thread is dead, and then ->join() and delete it.

fixes loading unit tests with "main" as the entry point.

This is like printf() but prints straight to the console instead of going
through the stdio library, the VFS and the device layer.

To be used for debugging outout in the kernel.

* 'master' of github.com:cloudius-systems/osv:
  interrupt manager: use range-based for loop instead of manually looping
  sched: optimize scanning the incoming_wakeups array
  sched: add an atomic cpu_set type

of the pci virtio config size to a function using the first.

Protect the array with a cpu_set (bit set -> corresponding queue non-empty).
This means we need to scan one word, instead of nr_cpus (plus of course all
the cpus for which an incoming is waiting).

Supporting up to 64 cpus for now.

This fixes an issue where a symbol exists in multiple objects; when just
one is loaded it is resolved to one of the modules, but after the second is
loaded, it resolves to the second.  To the program this appears as if the
address or contents of a static variable has changed.

In our case this was triggered by both statically and dynamically linking
a library.

The glibc headers define those as macros, need to undefine before declaring
as functions.

Found with mode=release.

Found with mode=release.

Atomic thread state and related work.

If we failed the initial trylock, that does not mean the mutex is locked,
as it could have been unlocked right before we grabbed the wait list lock.

Retry with the wait list lock held, as the unlock path must grab it before
unlocking.

Currently, we have an atomic _waiting state for a thread, and additional
non-atomic _on_runqueue and _terminated states.  This is problematic since
a ->wake() racing with a ->stop_wait() can cause a thread to be
simultaneously running and queued.

Fix by using a single atomic variable for all theses states.

When we migrate a thread, remove its timers from the cpu-local timer list,
and move them back when we complete migration.

A mutex will also call wait_until, which doesn't tolerate nesting.

debug output and do some order

It was triggered when there were debug prints in the middle of these functions that
cause context switch.