os_types: fix unsigned typedefs for MacOS
os_types: fix unsigned typedefs for MacOS

This effectively reverts f8ce071e1040c766157d630d920d6165d35fe422 which was
probably broken by 6449883ccacfee276ed9d99fa047342cdc51ab88.

xiph/ogg,ShiftMediaProject/ogg,xiph/ogg,ShiftMediaProject/ogg