Install the cmake files in an archecture independent location The build configuration in Debian builds only the header-only library; because of this, the resulting development files do not change depending on the architecture. On the other hand, the cmake config files generated by write_basic_package_version_file() by default do architecture checks (e.g. bits), which make the resulting config file not usable on all the architectures. Hence, pass ARCH_INDEPENDENT as additional parameter to avoid those checks. This was proposed upstream as https://github.com/ToruNiina/toml11/pull/257, and it was rejected as there are more build configurations possible, and upstream does not want to keep more build knobs.
