Comment 33 for bug 991493

Yes, we support 3.6 in 15.10. 3.7 is unsupported (and fails to build on i386 and powerpc).

> Nothing is put into the alternative system.

yes, intended. Use llvm-config-3.7 explicitly, or prefix your command with

    PATH=/usr/lib/llvm-3.7/bin:$PATH

> So if llvm-3.7-runtime, and llvm-3.7 dev are installed,
> there is really no way to pick a default to switch between revisions.

see above. you are wrong.

> If the installations at least added everything to alternatives,
> with the latest version given the highest priority, there would
> be a way to upgrade automatically, and manually select a desired version.

Wrong, this would lead to automatic breakage when changing LLVM versions. There are no two LLVM versions which are ABI and/or API compatible.