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

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

internal/sysfs/open_file_sun.go

@@ -5,12 +5,11 @@ package sysfs
 import (
 	"io/fs"
 	"os"
-	"syscall"
 
-	"github.com/tetratelabs/wazero/internal/platform"
+	"github.com/tetratelabs/wazero/experimental/sys"
 )
 
-func openFile(path string, flag int, perm fs.FileMode) (*os.File, syscall.Errno) {
+func openFile(path string, flag int, perm fs.FileMode) (*os.File, sys.Errno) {
 	f, err := os.OpenFile(path, flag, perm)
-	return f, platform.UnwrapOSError(err)
+	return f, sys.UnwrapOSError(err)
 }