new syscall package: manually maintained files and scripts.

new syscall package: manually maintained files and scripts.
auto-generated files and deletions are in another CL.

goals for new syscall:
	* automate as much as possible
	* do not let clients do unsafe things
	* use simple types (int not int64)
	* fewer files

the files are renamed from foo_amd64_linux to foo_linux_amd64,
both because it reads better (all the linux are related, all the amd64 less so)
and because it made it easier to replace the existing ones.

R=r
DELTA=2336  (2260 added, 6 deleted, 70 changed)
OCL=29709
CL=29723