[clang] nolock/noalloc attributes (PR #84983)

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Sirraide wrote:

> Just tried. In C mode, it works to do nothing about effect changes in isFunctionConversion (!).

I would maybe try going with that then for now (and maybe add a comment about that too); I’m not sure my function pointer example is really the same situation, but I remember finding an example that was analogous but for `noreturn` *somwhere* in the test cases, but I don’t remember where.

https://github.com/llvm/llvm-project/pull/84983