Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge from r161730:
o Set TP using inline assembly to avoid dead code elimination.
o Eliminate _tcb.

Merge from r161840:
Stylize: avoid using a global register variable.

Merge from r157461:
Simplify _get_curthread() and _tcb_ctor because libc and rtld now
already allocate thread pointer space in tls block for initial thread.

Merge from r177853:
Replace function _umtx_op with _umtx_op_err, the later function directly
returns errno, because errno can be mucked by user's signal handler and
most of pthread api heavily depends on errno to be correct, this change
should improve stability of the thread library.

MFC after: 1 week

Merge from tbemd, with a small amount of rework:
For all libthr contexts, use ${MACHINE_CPUARCH}
for all libc contexts, use ${MACHINE_ARCH} if it exists, otherwise use
${MACHINE_CPUARCH}
Move some common code up a layer (the .PATH statement was the same in
all the arch submakefiles).

# Hope she hasn't busted powerpc64 with this...

style.Makefile(5)

style(9)

- Remove variable _thr_scope_system, all threads are system scope.
- Rename _thr_smp_cpus to boolean variable _thr_is_smp.
- Define CPU_SPINWAIT macro for each arch, only X86 supports it.

Import my recent 1:1 threading working. some features improved includes:
1. fast simple type mutex.
2. __thread tls works.
3. asynchronous cancellation works ( using signal ).
4. thread synchronization is fully based on umtx, mainly, condition
variable and other synchronization objects were rewritten by using
umtx directly. those objects can be shared between processes via
shared memory, it has to change ABI which does not happen yet.
5. default stack size is increased to 1M on 32 bits platform, 2M for
64 bits platform.
As the result, some mysql super-smack benchmarks show performance is
improved massivly.

Okayed by: jeff, mtm, rwatson, scottl

Return gracefully, rather than aborting, when the maximum concurrent
threads per process has been reached. Return EAGAIN, as per spec.

Approved by: re/blanket libthr

- Pass a ucontext_t to _set_curthread. If non-NULL the new thread is set
as curthread in the new context, so that it will be set automatically when
the thread is switched to. This fixes a race where we'd run for a little
while with curthread unset in _thread_start.

Reviewed by: jeff

Implement _get_curthread and _set_curthread. This is especially easy.

Add MD makefile.