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

[David Blaikie via llvm-commits]

dwblaikie wrote:

In general, I think we should disable any compiler warnings that produce would otherwise encourage us to contort our code in ways that don't make it more readable - and I worry this warning will do that at some point, but this particular instance I don't mind/seems nice enough.

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