int/linux: add/use Dup3, Open, Openat

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/cmd/seccompagent/seccompagent.go

@@ -14,6 +14,7 @@ import (
 	"strings"
 
 	securejoin "github.com/cyphar/filepath-securejoin"
+	"github.com/opencontainers/runc/internal/linux"
 	"github.com/opencontainers/runtime-spec/specs-go"
 	libseccomp "github.com/seccomp/libseccomp-golang"
 	"github.com/sirupsen/logrus"
@@ -124,7 +125,7 @@ func handleNewMessage(sockfd int) (uintptr, string, error) {
 func readArgString(pid uint32, offset int64) (string, error) {
 	buffer := make([]byte, 4096) // PATH_MAX
 
-	memfd, err := unix.Open(fmt.Sprintf("/proc/%d/mem", pid), unix.O_RDONLY, 0o777)
+	memfd, err := linux.Open(fmt.Sprintf("/proc/%d/mem", pid), unix.O_RDONLY, 0o777)
 	if err != nil {
 		return "", err
 	}