[clang] [NFC] Use `const&` avoiding copies (PR #90334)

[Danny Mösch via cfe-commits]

SimplyDanny wrote:

> This change seems to be unrelated to the platform, and I don't think it's the change that caused the CI error. From the compiled log, it seems that there is not enough memory space. <img alt="3eb6d694feb6b9b289d0fff72552fb88" width="1499" src="https://private-user-images.githubusercontent.com/22370779/327938136-d1acbd6b-45e4-46c0-b297-9d0a8f8abedb.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.QXRMCiD3fniqXEUHLPOAjqAcfAM3jDgBr3ZFcNQ4jNc">

Okay, that's good news. I wasn't sure because I've not found any other builds to fail like this and mine reported failure twice. But indeed I face the same excessive RAM consumption when building the `flang` target locally on `main`.

https://github.com/llvm/llvm-project/pull/90334