Here is the big 2.5.21 x86-64 sync patch. It only touches arch/x86_64
and include/asm-x86_64. It requires a few other changes that I'm sending
in separate mail.

Changes:
- merge wit 2.5.21
- merge from 2.5.21/i386 (new PCI code, new LDT code etc.)
- sync with 2.4-x86_64 tree.
- minor updates to 32bit emulation
- better early console; including serial support.
- now set up dummy PDA for booting to avoid problems
- Fix GS reloading in context switch one instruction race
- Remove hardcoded names from mpparse code
- Fix inline assembly for RAID-5 xor (similar change needed for i386)
- Real per cpu data support based on PDA field
- Cleanup of offset.c generation requested by Kai: it only puts structure
  offsets into offset.h now.
- Fix i387 fxsave signal frame problems.
- Add uname emulation via personality ("linux32")
- New SSE optimized checksum-copy, copy*user, memcpy, clear_page, copy_page
  functions. Other tunings/cleanups in checksum and other user memory
  access function.
- check if exception table is really sorted
- Cleanups in page table handling in preparation of non executable pages
  support.
- Cleanup PDA access to not require offset.h (thanks to kai for kicking me
  to this)
- use long long for u64/s64 to avoid more warnings
- remove CONFIG_ISA
- fix various bugs and other cleanups