Initial support for LLVM 20 (#57352)
For LLVM 20, we still need to deal with
https://github.com/JuliaLang/julia/issues/55844,
https://github.com/JuliaLang/julia/issues/57021 and get the LLVM 19 PR
in.
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Co-authored-by: Mosè Giordano <765740+giordano@users.noreply.github.com>
