{amd64,i386}/SYS.h: add _SYSCALL and _SYSCALL_BODY

[brooks]

Summary

Add a _SYSCALL(name) which calls the SYS_name syscall. Use it to add a
_SYSCALL_BODY() macro which invokes the syscall and calls cerror as
required. Use the latter to implement PSEUDO() and RSYSCALL().

Sponsored by: DARPA

[brooks]

This is part of a set of changes I've posted at https://github.com/brooksdavis/freebsd/tree/SYS.h-unification. I've done basic smoke testing of amd64 under qemu, i386 might need more testing.

[markj]

lib/libc/amd64/SYS.h

39

45

We're inconsistent about whether the macro ends with a semicolon.

It would also be more consistent to keep one instruction per line.

lib/libc/i386/SYS.h

39

[brooks]

Address formatting issues pointed out by @markj