Fix and cleanups of linux PlatformDefs.h

Most important changes:
* use `int32_t` instead of `int` for `DWORD` and for `__int32`
* use `int16_t` instead of `short` for `WORD` and for `__int16`
* use `intptr_t` instead of `long` for `LONG_PTR` (Windows use `__int3264` for it)