'RELENG_6_0_0_RELEASE'.

This commit was manufactured to restore the state of the 6.0-RELEASE image.

This changes things like whitespace, inconsistent use of #ifndef vs
#if !defined(), different macro argument orders, mismatched comments, etc.

place.

This moves the dependency on GCC's and other compiler's features into
the central sys/cdefs.h file, while the individual source files can
then refer to #ifdef __COMPILER_FEATURE_FOO where they by now used to
refer to #if __GNUC__ > 3.1415 && __BARC__ <= 42.

By now, GCC and ICC (the Intel compiler) have been actively tested on
IA32 platforms by netchild.  Extension to other compilers is supposed
to be possible, of course.

Submitted by:	netchild
Reviewed by:	various developers on arch@, some time ago

unintended local change.  Change Xurthread back to curthread.

the compiler having to parse and optimize the PCPU_GET(curthread) so often.
__curthread() is an inline optimized version of PCPU_GET(curthread) that
knows that pc_curthread is at offset zero in the pcpu struct.  Add a
CTASSERT() to catch any possible changes to this.  This accounts for
just over a 1% wall clock speedup for total kernel compile/link time,
and 20% compile time speedup on some specific files depending on which
compile options are used.

Approved by:  re (jhb)

- This is heavily derived from John Baldwin's apic/pci cleanup on i386.
- I have completely rewritten or drastically cleaned up some other parts.
  (in particular, bootstrap)
- This is still a WIP.  It seems that there are some highly bogus bioses
  on nVidia nForce3-150 boards.  I can't stress how broken these boards
  are.  I have a workaround in mind, but right now the Asus SK8N is broken.
  The Gigabyte K8NPro (nVidia based) is also mind-numbingly hosed.
- Most of my testing has been with SCHED_ULE.  SCHED_4BSD works.
- the apic and acpi components are 'standard'.
- If you have an nVidia nForce3-150 board, you are stuck with 'device
  atpic' in addition, because they somehow managed to forget to connect the
  8254 timer to the apic, even though its in the same silicon!  ARGH!
  This directly violates the ACPI spec.

and by not using a statement-expression for the non-expression
__PCPU_SET().

PCPU_MD_FIELDS).

dereference the softc.

a heavily stripped down FreeBSD/i386 (brutally stripped down actually) to
attempt to get a stable base to start from.  There is a lot missing still.
Worth noting:
- The kernel runs at 1GB in order to cheat with the pmap code.  pmap uses
  a variation of the PAE code in order to avoid having to worry about 4
  levels of page tables yet.
- It boots in 64 bit "long mode" with a tiny trampoline embedded in the
  i386 loader.  This simplifies locore.s greatly.
- There are still quite a few fragments of i386-specific code that have
  not been translated yet, and some that I cheated and wrote dumb C
  versions of (bcopy etc).
- It has both int 0x80 for syscalls (but using registers for argument
  passing, as is native on the amd64 ABI), and the 'syscall' instruction
  for syscalls.  int 0x80 preserves all registers, 'syscall' does not.
- I have tried to minimize looking at the NetBSD code, except in a couple
  of places (eg: to find which register they use to replace the trashed
  %rcx register in the syscall instruction).  As a result, there is not a
  lot of similarity.  I did look at NetBSD a few times while debugging to
  get some ideas about what I might have done wrong in my first attempt.