FileStat size integer overflow

`sys.FileSystem.stat(path).size` returns a negative number for a file more than 2.1 GB long

The problem is all values from `stat` are cast to 4 byte int:
`STATF(size);` [Sys.cpp#L410](https://github.com/HaxeFoundation/hxcpp/blob/master/src/hx/libs/std/Sys.cpp#L410)
`#define STATF(f) o->Add(HX_CSTRING(#f),(int)(s.st_##f))` [Sys.cpp#L369](https://github.com/HaxeFoundation/hxcpp/blob/master/src/hx/libs/std/Sys.cpp#L369)

(also mode is set twice)