Move every platform macro ifdef into platforms.

## Brief feature description

The `iceoryx_hoofs/platforms` should be the only place where platform specific code should be handled. The iceoryx code base should then use the `platform` abstraction to write platform independent code - it shouldn't be handled directly in the implementation.

## Detailed information
Here is an incomplete list (must be extended later) of platform dependent code outside of `iceoryx_hoofs/platforms`

- [ ] `iceoryx_hoofs/source/posix_wrapper/unix_domain_socket.cpp`