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

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

internal/sysfs/rename_windows.go

@@ -4,10 +4,10 @@ import (
 	"os"
 	"syscall"
 
-	"github.com/tetratelabs/wazero/internal/platform"
+	"github.com/tetratelabs/wazero/experimental/sys"
 )
 
-func rename(from, to string) syscall.Errno {
+func rename(from, to string) sys.Errno {
 	if from == to {
 		return 0
 	}
@@ -18,7 +18,7 @@ func rename(from, to string) syscall.Errno {
 	} else {
 		fromIsDir = fromStat.Mode.IsDir()
 	}
-	if toStat, errno := stat(to); errno == syscall.ENOENT {
+	if toStat, errno := stat(to); errno == sys.ENOENT {
 		return syscallRename(from, to) // file or dir to not-exist is ok
 	} else if errno != 0 {
 		return errno // failed to stat to
@@ -29,20 +29,20 @@ func rename(from, to string) syscall.Errno {
 	// Now, handle known cases
 	switch {
 	case !fromIsDir && toIsDir: // file to dir
-		return syscall.EISDIR
+		return sys.EISDIR
 	case !fromIsDir && !toIsDir: // file to file
 		// Use os.Rename instead of syscall.Rename to overwrite a file.
 		// This uses MoveFileEx instead of MoveFile (used by syscall.Rename).
-		return platform.UnwrapOSError(os.Rename(from, to))
+		return sys.UnwrapOSError(os.Rename(from, to))
 	case fromIsDir && !toIsDir: // dir to file
-		return syscall.ENOTDIR
+		return sys.ENOTDIR
 	default: // dir to dir
 
 		// We can't tell if a directory is empty or not, via stat information.
 		// Reading the directory is expensive, as it can buffer large amounts
 		// of data on fail. Instead, speculatively try to remove the directory.
 		// This is only one syscall and won't buffer anything.
-		if errno := rmdir(to); errno == 0 || errno == syscall.ENOENT {
+		if errno := rmdir(to); errno == 0 || errno == sys.ENOENT {
 			return syscallRename(from, to)
 		} else {
 			return errno
@@ -50,6 +50,6 @@ func rename(from, to string) syscall.Errno {
 	}
 }
 
-func syscallRename(from string, to string) syscall.Errno {
-	return platform.UnwrapOSError(syscall.Rename(from, to))
+func syscallRename(from string, to string) sys.Errno {
+	return sys.UnwrapOSError(syscall.Rename(from, to))
 }