AMD64-01-amd64: the first commit of a series of 6 commits for the amd64 port 
This commit includes header files for amd64 cpu that are in sys/cpu/amd64/include.

The #1 task to port for amd64 is to get the world/kernel cross-compiled for the
64-bit target. This involves creating a platform and cpu target for the build. The 
skeleton infrastructure for the cpu and platform is the sys/cpu/amd64 folder and the
sys/platform/pc64 folder. 

The first stage of this #1 task is to have the world cross-build.
It includes the building of cross toolchains, the libraries and the world. 
This series of commits makes the world cross-build (buildworld) for the amd64 port with
these environment variables: TARGET_CPU=amd64; TARGET_PLATFORM=pc64; NO_GCC41=1
 
This is the first commit: resurrect headers for sys/cpu/amd64/include from cvs Attic;
patch and mark them as CPU specific

AMD64-02-pc64: resurrect headers for sys/platform/pc64/include from CVS Attic; patch and
mark them as platform specific

AMD64-03-libc: libc amd64 port in /lib/libc/amd64/, including gen/mcontext.S sys/asmcontext.c
and related Makefile*. 

AMD64-04-gdb: gdb (gnu/usr.bin/gdb/libgdb) patch that bypass calling into functions in bsd_kvm.c

AMD64-05-MACHINE: a Makefile workaround to define the MACHINE macro for the source 
preprocessing in man, makewhatis and xlint

AMD64-06-misc: for amd64 define in disklabel32.h and function header in in6.h  
