Add conditional build files for unix.Access.

This will allow library to be built on windows.

access_unix.go

@@ -0,0 +1,9 @@
+// +build darwin freebsd linux netbsd openbsd
+
+package adb
+
+import "golang.org/x/sys/unix"
+
+func access(path string) error {
+	return unix.Access(path, unix.X_OK)
+}

access_win.go

@@ -0,0 +1,15 @@
+// +build windows
+
+package adb
+
+import (
+	"errors"
+	"strings"
+)
+
+func access(path string) error {
+	if strings.Contains(path, ".exe") {
+		return nil
+	}
+	return errors.New("not an executable")
+}

server.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/zach-klippenstein/goadb/internal/errors"
 	"github.com/zach-klippenstein/goadb/wire"
-	"golang.org/x/sys/unix"
 )
 
 const (
@@ -137,7 +136,7 @@ var localFilesystem = &filesystem{
 		if !info.Mode().IsRegular() {
 			return stderrors.New("not a regular file")
 		}
-		return unix.Access(path, unix.X_OK)
+		return Access(path)
 	},
 	CmdCombinedOutput: func(name string, arg ...string) ([]byte, error) {
 		return exec.Command(name, arg...).CombinedOutput()

unix.go

@@ -0,0 +1,11 @@
+package adb
+
+/*
+Exported Access function calls private access function.
+Implementation for private access function is provided in
+access_win.go for windows and
+access_unix.go for unix
+*/
+func Access(path string) error {
+	return access(path)
+}