Add LLVM's LICENSE.txt file to the monorepo root

[arphaman]

Summary

The llvm-project monorepo (https://github.com/llvm/llvm-project) is currently missing a top-level license file. I think it should have one though.

[probinson]

This is imposing a requirement on how downstream projects manage their license files. I'm not saying we can't (eventually) do it this way, but I'm quite sure that's not how Sony handles it right now.

[jyknight]

I agree, it should have one, especially once we stop supporting separate checkouts, and hopefully can remove redundant copies in other places.

@probinson I don't understand what you mean -- what's the issue you see with adding this file right now?

[mehdi_amini]

The motivation is unclear to me at the moment? Why is it a good thing?

[probinson]

In D64875#1590152, @jyknight wrote:

@probinson I don't understand what you mean -- what's the issue you see with adding this file right now?

The LICENSE.txt file asserts something about the directory tree, at the top level, which didn't used to be asserted. I know that my internal repo fails to comply with the assertion in that LICENSE.txt file. Therefore I don't want it to happen without the right lawyers involved.

To an engineer this looks like an obvious "refactoring" but this is not code, people, this is lawyer stuff. The Foundation tiptoes very carefully when it comes to the license and I don't think engineers should be hacking on what the Foundation asserts about the legal status of the repo, without the Foundation saying this is the right way to go.

[arphaman]

I will abandon this patch and will try to reach out to the Foundation for guidance instead. I offered more rationale on why we think this is important on llvm-dev:

http://lists.llvm.org/pipermail/llvm-dev/2019-July/134038.html

LICENSE.txt

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