Remove the contents of Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64 and re-run the commands starting with Setup.sh.
This is on Ubuntu 20.04.3 LTS in a git checkout that previously built 4.26 and I wanted a 4.27 preview which was using different clang libs. I think it was confused by multiple libs being at that location.