[llvm] [mlir] [MLIR][Python] reland stubgen (PR #157853)

[Maksim Levental via llvm-commits]

makslevental wrote:

> Thanks! `$ pip install nanobind --upgrade` did the trick! Is this something we could detect and error out in CMake?

The error, which probably surfaced by `nanobind` itself, was hidden because in https://github.com/llvm/llvm-project/pull/157583 I `--quiet`ed output to prevent spamming during build 😄 . The "correct" solution is to not `--quiet` that output and instead fix the spamming using `DEPFILE` (which is done in this patch).

> Also: does it mean that the standalone example didn't catch any issue? Can we update it to provide more coverage representative of the issues that the other folks hit?

Yes this has all been very unfortunate and partially due to `standalone` not being a robust enough test of build paths. I fixed some stuff here https://github.com/llvm/llvm-project/pull/156197 but I would like to fix more (see https://github.com/llvm/llvm-project/pull/157944, which isn't ready yet).

FYI: this patch can't land due to complication with IREE so I'm reverting to draft. I've narrowed the feature and will shortly release https://github.com/llvm/llvm-project/pull/157930 for review.

https://github.com/llvm/llvm-project/pull/157853