[llvm] [DTLTO] [LLVM] Initial DTLTO cache implementation (PR #156433)

[Teresa Johnson via llvm-commits]

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teresajohnson wrote:

The return type is confusing, since you always return success but update Err to something other than success when there is an error. Can you change this function to return the error when one occurs and invoke joinErrors in the caller? I.e. structure like InProcessThinBackend::runThinLTOBackendThread. Suggestions to that effect below.

https://github.com/llvm/llvm-project/pull/156433