add RealOSType and also set unknown ostype

Pilz/Runtime/OSType.vb

@@ -1,6 +1,7 @@
 Namespace Runtime
 
     Public Enum OSType
+        Unknown
         Windows
         Linux
         OSX

Pilz/Runtime/RuntimeInformationsEx.vb

@@ -1,4 +1,5 @@
-Imports System.Runtime.InteropServices
+Imports System.IO
+Imports System.Runtime.InteropServices
 
 Namespace Runtime
 
@@ -16,6 +17,8 @@ Namespace Runtime
                             t = OSType.Linux
                         Case RuntimeInformation.IsOSPlatform(OSPlatform.OSX)
                             t = OSType.OSX
+                        Case Else
+                            t = OSType.Unknown
                     End Select
                 End If
 
@@ -23,6 +26,35 @@ Namespace Runtime
             End Get
         End Property
 
+        Public ReadOnly Property RealOSType As OSType
+            Get
+                Static t As OSType? = Nothing
+
+                If t Is Nothing Then
+                    Dim windir As String = Environment.GetEnvironmentVariable("windir")
+
+                    If Not String.IsNullOrEmpty(windir) AndAlso windir.Contains("\") AndAlso Directory.Exists(windir) Then
+                        t = OSType.Windows
+                    ElseIf File.Exists("/proc/sys/kernel/ostype") Then
+                        Dim osTypeString As String = File.ReadAllText("/proc/sys/kernel/ostype")
+                        If osTypeString.StartsWith("Linux", StringComparison.OrdinalIgnoreCase) Then
+                            ' Note: Android gets here too
+                            t = OSType.Linux
+                        Else
+                            t = OSType.Unknown
+                        End If
+                    ElseIf File.Exists("/System/Library/CoreServices/SystemVersion.plist") Then
+                        ' Note: iOS gets here too
+                        t = OSType.OSX
+                    Else
+                        t = OSType.Unknown
+                    End If
+                End If
+
+                Return t
+            End Get
+        End Property
+
     End Module
 
 End Namespace