llvm: the bottle needs the Apple Command Line Tools to be installed.
You can install them, if desired, with:
xcode-select --install
If you're feeling brave, you can try to install from source with:
brew install --build-from-source llvm
It is expected behaviour that most formulae will fail to build from source.
It is expected behaviour that Homebrew will be buggy and slow when building from source.
Do not create any issues about failures building from source on Homebrew's GitHub repositories.
Do not create any issues building from source even if you think this message is unrelated.
Any opened issues will be immediately closed without response.
Do not ask for help from Homebrew or its maintainers on social media.
You may ask for help building from source in Homebrew's discussions but are unlikely to receive a response.
If building from source fails, try to figure out the problem yourself and submit a fix as a pull request.
We will review it but may or may not accept it.