CompatHelper: bump compat for "LLVM" to "4"

[github-actions[bot]]

This pull request changes the compat entry for the LLVM package from 3.6 to 3.6, 4.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.