Clang-21 and Clang-22 fail for mixed Fortran and C builds

See this example build failure: https://github.com/bertcarnell/nleqslv/actions/runs/23829406443/job/69459434847#step:6:1 The key error is that -lFortanRuntime is not found. The name has changed, and it is no longer installed in the LLVM-21 and 22 builds. It now needs to be built as a separate runtime library which is not part of the apt package install.