danc gave me information about how he was able to get the current freedom-u-sdk, which works on Ubuntu 16.04, to build an image and tools under Fedora 28. The main issues are that Fedora 28 can’t build the legacy buildroot that is supplied with the SDK. The newer buildroot needs fixing, as does the configuration. All of the necessary steps, including a complicated git submodule dance are shown in a little page I wrote for myself.
https://github.com/dpreed/RISCV-work/wiki/freedom-u-sdk-fedora28