avoid hardcoded folders when creating packages for distributions

In particular this:

```
if("${os_name}" STREQUAL "clear-linux-os")
    # clear-linux-os distribution avoids /etc for distribution defaults.
    # Set this variable explicitly before including GNUInstallDirs.
    set(CMAKE_INSTALL_SYSCONFDIR "usr/share/defaults/etc")
endif()
```
If Clear-Linux is not setting SYSCONFDIR file a bug with them. 