[clang] [clang][docs] Fix unhandled Error in LibTooling examples (PR #186589)

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Sirraide wrote:

> Continues the work from #98129 (approved by @nickhuang99 and @Sirraide but never merged)

Ah, my bad, it seems that pr just got lost in my inbox and no-one ever pinged me about it... in situations like these, it’s better to just ping the approver on the original pr. Since the changes are literally the same as in this pr I think we should just merge #98129.

https://github.com/llvm/llvm-project/pull/186589