'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

 - p_sflag was mostly protected by PROC_LOCK rather than the PROC_SLOCK or
   previously the sched_lock.  These bugs have existed for some time.
 - Allow swapout to try each thread in a process individually and then
   swapin the whole process if any of these fail.  This allows us to move
   most scheduler related swap flags into td_flags.
 - Keep ki_sflag for backwards compat but change all in source tools to
   use the new and more correct location of P_INMEM.

Reported by:	pho
Reviewed by:	attilio, kib
Approved by:	re (kensmith)

- Reorder the events in exit(2) slightly so that we trigger the S_EXIT
  stop event earlier.  After we have signalled that, we set P_WEXIT and
  then wait for any processes with a hold on the vmspace via PHOLD to
  release it.  PHOLD now KASSERT()'s that P_WEXIT is clear when it is
  invoked, and PRELE now does a wakeup if P_WEXIT is set and p_lock drops
  to zero.
- Change proc_rwmem() to require that the processing read from has its
  vmspace held via PHOLD by the caller and get rid of all the junk to
  screw around with the vmspace reference count as we no longer need it.
- In ptrace() and pseudofs(), treat a process with P_WEXIT set as if it
  doesn't exist.
- Only do one PHOLD in kern_ptrace() now, and do it earlier so it covers
  FIX_SSTEP() (since on alpha at least this can end up calling proc_rwmem()
  to clear an earlier single-step simualted via a breakpoint).  We only
  do one to avoid races.  Also, by making the EINVAL error for unknown
  requests be part of the default: case in the switch, the various
  switch cases can now just break out to return which removes a _lot_ of
  duplicated PRELE and proc unlocks, etc.  Also, it fixes at least one bug
  where a LWP ptrace command could return EINVAL with the proc lock still
  held.
- Changed the locking for ptrace_single_step(), ptrace_set_pc(), and
  ptrace_clear_single_step() to always be called with the proc lock
  held (it was a mixed bag previously).  Alpha and arm have to drop
  the lock while the mess around with breakpoints, but other archs
  avoid extra lock release/acquires in ptrace().  I did have to fix a
  couple of other consumers in kern_kse and a few other places to
  hold the proc lock and PHOLD.

Tested by:	ps (1 mostly, but some bits of 2-4 as well)
MFC after:	1 week

as they are already default for I686_CPU for almost 3 years, and
CPU_DISABLE_SSE always disables it.  On the other hand, CPU_ENABLE_SSE
does not work for I486_CPU and I586_CPU.

This commit has:
	- Removed the option from conf/options.*
	- Removed the option and comments from MD NOTES files
	- Simplified the CPU_ENABLE_SSE ifdef's so they don't
	  deal with CPU_ENABLE_SSE from kernel configuration. (*)

For most users, this commit should be largely no-op.  If you used to
place CPU_ENABLE_SSE into your kernel configuration for some reason,
it is time to remove it.

(*) The ifdef's of CPU_ENABLE_SSE are not removed at this point, since
    we need to change it to !defined(CPU_DISABLE_SSE) && defined(I686_CPU),
    not just !defined(CPU_DISABLE_SSE), if we really want to do so.

Discussed on:	-arch
Approved by:	re (scottl)

  1. Process p1 is currently being swapped in.
  2. Process p2 calls linux_ptrace(PTRACE_GETFPXREGS, p1_pid, ...)
  3. After acquiring a reference to FIRST_THREAD_IN_PROC(p1),
     p2 blocks in faultin() while p1 finishes being swapped in.
     This means p2 won't get back the lock on p1 until after p1's
     threads are runnable.
  4. After p1 is swapped in, the first thread in p1 exits.
  5. p2 now uses its dangling reference to p1's first thread.

in <sys/cdefs.h> for compilers without support for inline.

safe to do so.

a duplicate P_TRACED check.

Submitted by:	marcel