wasip2: add stubs to get internal/syscall/unix to work

This fixes lots of broken tests in stdlib packages in Go 1.24.

src/syscall/syscall_libc.go

@@ -233,6 +233,10 @@ func (w WaitStatus) Continued() bool    { return false }
 func (w WaitStatus) StopSignal() Signal { return 0 }
 func (w WaitStatus) TrapCause() int     { return 0 }
 
+// Purely here for compatibility.
+type Rusage struct {
+}
+
 // since rusage is quite a big struct and we stub it out anyway no need to define it here
 func Wait4(pid int, wstatus *WaitStatus, options int, rusage uintptr) (wpid int, err error) {
 	return 0, ENOSYS // TODO

src/syscall/syscall_libc_wasi.go

@@ -120,8 +120,11 @@ const (
 	SYS_FCNTL64
 	SYS_FSTATAT64
 	SYS_IOCTL
+	SYS_MKDIRAT
 	SYS_OPENAT
+	SYS_READLINKAT
 	SYS_UNLINKAT
+	SYS_WAITID
 	PATH_MAX = 4096
 )