Fix for missing `GetTickCount64` in lower versions of Delphi

[edwinyzh]

Hi, thanks for this excellent lib!
The following code is for fixing the tgputtysftp.pas compilation issue under XE 4 and lower, you can add the code right below implementation:

// Edwin Yip: XE4 (CompilerVersion=25.0) doesn't have GetTickCount64 defined in the `Windows` unit, don't know about other higher versions...
{$IF CompilerVersion < 26.0}
function GetTickCount64: UInt64; stdcall; external kernel32 name 'GetTickCount64';
{$IFEND}