Unix platform support to support FreeBSD etc.

[elfenpiff]

Brief feature description

At the moment the unix platform is not supported at all because the necessary variable in the CMakeLists.txt are not set and some minor Linux specific macros are used instead of the POSIX ones.
To adjust this one has to set the ICEORYX_CXX_STANDARD, the platform files and write the code really posix compliant.

With this we could support then platforms like FreeBSD, OpenBSD etc.

Another advantage would be that we test everything on an alternative POSIX platform which reduces the occurrence of undefined behavior or misuse.