Auto merge of #118936 - nikic:update-llvm-18, r=cuviper

Update to LLVM 17.0.6

This is a rebase on the final LLVM 17 release.

Includes the RISCV fix requested in rust-lang/llvm-project#157 (and I think this is also the only change in this release that is relevant to rustc).

r? `@cuviper`

Fixes #117902

Author: bors