Correct the abi.zig header (and the matching build.zig / README lines): the syscall ABI
is the private contract between the kernel and the runtime library, not something every
user program speaks. danos applications call the `runtime` (the stable, danos-native
ABI); the runtime is the only thing that issues system calls, and POSIX layers over the
runtime — the same split as libSystem on macOS or win32 over the NT syscalls. The call
numbers here are an implementation detail the runtime hides and may renumber, not a
public interface.
Daniel Samson
3ec2d1828a