[clang] [lld] [llvm] [mlir] [polly] [SetVector] Make SetVector::insert consistent (NFC) (PR #232372)

[Alexis Engelke via cfe-commits]

https://github.com/aengelke commented:

> It's a header-only change, that should be trivially inlined and DCE'd well before any LTO?

Could also be a GCC vs Clang difference (stage1 Clang is built by GCC, stage2 is clang-built-clang).

https://github.com/llvm/llvm-project/pull/232372