[clang] [lld] [llvm] Integrated Distributed ThinLTO (DTLTO): Initial support (PR #126654)

[via cfe-commits]

bd1976bris wrote:

Reviewers have suggested that smaller PRs be created to facilitate detailed reviews while keeping this one around to provide an overall picture and facilitate discussion of high-level design (see [this ongoing discussion](https://github.com/llvm/llvm-project/pull/126654#discussion_r1951679978)). I have created [PR #127749](https://github.com/llvm/llvm-project/pull/127749) to collect detailed review comments for the parts related to LLVM and have added those who commented here as reviewers.
I will do my best to keep this PR up to date with suggestions from "child" PRs such as [PR #127749](https://github.com/llvm/llvm-project/pull/127749).

Note that I have changed the name of this PR to indicate that it provides an overview of DTLTO to avoid confusion.

Thanks again for all your input!

https://github.com/llvm/llvm-project/pull/126654