Set sensible defaults for Windows installations

Non-packaged execution will need this to be overridden anyway, and it
avoids a surprise "Drop state data into the current working directory"
event.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

util/appdefaults/appdefaults_windows.go

@@ -1,9 +1,17 @@
 package appdefaults
 
+import (
+	"os"
+	"path/filepath"
+)
+
 const (
-	Address   = "npipe:////./pipe/buildkitd"
-	Root      = ".buildstate"
-	ConfigDir = ""
+	Address = "npipe:////./pipe/buildkitd"
+)
+
+var (
+	Root      = filepath.Join(os.Getenv("ProgramData"), "buildkitd", ".buildstate")
+	ConfigDir = filepath.Join(os.Getenv("ProgramData"), "buildkitd")
 )
 
 func UserAddress() string {