This can occur due to linker ICF and stable sort will ensure the results
are stable.
No explicit/new test coverage, because nondeterminism is non-testable.
It should already be covered by the DWARFDebugLineTest that was failing
some internal testing on an ARM machine which might've been what changed
the sort order. But `llvm::sort` also deliberately randomizes the
contents (under EXPENSIVE_CHECKS) so I'd have expected failures to show
up in any EXPENSIVE_CHECKS Build...
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