Rollup merge of #145073 - ZuseZ4:autodiff-llvm-21, r=jieyouxu

update enzyme submodule to handle llvm 21

This currently has a fix / workaround in our local rust-lang/Enzyme fork, which is needed to unblock a few people contributing to std::autodiff. It also permanently disables a component (BCLoader) which we shouldn't need on the rust side, hence saving a bit of compile time and disk space.

Once upstream Enzyme (EnzymeAD/Enzyme) fixed llvm-21 support I'll probably make another pr to drop our local patch.

Author: Zalathar