adds experimental sys.Errno to begin decoupling from the syscall package (#1582)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/sysfs/sock.go

@@ -3,8 +3,8 @@ package sysfs
 import (
 	"net"
 	"os"
-	"syscall"
 
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
 	"github.com/tetratelabs/wazero/internal/fsapi"
 	socketapi "github.com/tetratelabs/wazero/internal/sock"
 	"github.com/tetratelabs/wazero/sys"
@@ -24,14 +24,14 @@ type baseSockFile struct {
 var _ fsapi.File = (*baseSockFile)(nil)
 
 // IsDir implements the same method as documented on File.IsDir
-func (*baseSockFile) IsDir() (bool, syscall.Errno) {
+func (*baseSockFile) IsDir() (bool, experimentalsys.Errno) {
 	// We need to override this method because WASI-libc prestats the FD
 	// and the default impl returns ENOSYS otherwise.
 	return false, 0
 }
 
 // Stat implements the same method as documented on File.Stat
-func (f *baseSockFile) Stat() (fs sys.Stat_t, errno syscall.Errno) {
+func (f *baseSockFile) Stat() (fs sys.Stat_t, errno experimentalsys.Errno) {
 	// The mode is not really important, but it should be neither a regular file nor a directory.
 	fs.Mode = os.ModeIrregular
 	return