[clang] [llvm] Remove remaining uses of Instruction-constructors that insert before another Instruction (PR #85981)

[Orlando Cazalet-Hyams via cfe-commits]

https://github.com/OCHyams approved this pull request.

LGTM if this is clang-formatted (I can't tell). Plus one small inline nit - I think it's fine either way.

https://github.com/llvm/llvm-project/pull/85981