`type nr = enum i64 { READ, WRITE, OPEN, ... }`. syscall0..4 take
`num: nr` so the wrong-arg-order trap is now a compile error
(`syscall1(0i64, ...)` no longer typechecks — it has to be
`syscall1(nr.READ, ...)`).
Internal-only (callers outside os.ww never touched the constants),
so no external API change. ABI is unchanged: nr's storage is i64
and rt_syscall's RDI is unchanged.
The selfhost combined.ww files regenerate as a side effect of
`make wwstage`.