Added enum declaration for LongPtr

[SSlinky]

Enums were broken when declaring Private Enum LongPtr. This is used as faux type when working with VBA6 so that types are consistent in code, e.g.

#If VBA7 Then
  Private Declare PtrSafe Function GetDesktopWindow Lib "user32" () As LongPtr
#Else
  Private Enum LongPtr
    [_]
  End Enum
  Private Declare Function GetDesktopWindow Lib "user32" () As LongPtr
#End If

Fixes #19