SysUtils type helper a new feature, there may be errors, check before using.
For example this code in Windows 7, x64, Lazarus 64 bit:
{$APPTYPE CONSOLE}
program Project1;
uses SysUtils;
var
X: Int64;
begin
Writeln(X.MaxValue.ToString);
Writeln(IntToStr(High(X)));
Readln;
end.
The result is wrong:
2147483647
9223372036854775807
Add bug
http://bugs.freepascal.org/view.php?id=31521