I would like to extend @Felipe excellent answer; if it doesn't work even with running
>>> softwareupdate --all --install --force
Software Update Tool
Finding available software
No updates are available.
...following the wisdom of the "homebrew doctor" solves it, i.e. remove and reinstall:
sudo rm -rf /Library/Developer/CommandLineTools
sudo xcode-select --install
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…