[llvm] [DebugInfo] Fix compact DWARF expression failure handling (PR #213391)

[Scott Linder via llvm-commits]

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slinder1 wrote:

This comment is over-fit to the immediate thing we are fixing. The place to document the fact that the callback should not have side effects is on `printDwarfExpressionCompact` itself, IMO

https://github.com/llvm/llvm-project/pull/213391