[llvm] [LTO] Turn ImportListsTy into a proper class (NFC) (PR #106427)

[Nikita Popov via llvm-commits]

nikic wrote:

After some further investigation, this issue occurs when empty or mostly empty (e.g. module inline asm only) modules are part of the thin link.

And the reason why LLVM did not hit this problem is this code: https://github.com/llvm/llvm-project/blob/0dd56858fe188419182a57d0e03c8cd0aa693867/llvm/lib/LTO/ThinLTOCodeGenerator.cpp#L1102-L1111

So LLVM's solution here was to force-initialize all map entries, while Rust's solution was to use read-only access to the maps.

https://github.com/llvm/llvm-project/pull/106427