[llvm] [Support] Avoid warning about possibly uninitialized variable in format_provider (PR #95704)

[Chandler Carruth via llvm-commits]

chandlerc wrote:

> @chandlerc Could you approve the workflow for this PR?

I'm not that up-to-date with LLVM these days, probably better for @dwblaikie or someone else more active to look at this.

https://github.com/llvm/llvm-project/pull/95704