Changes

Revert "[RISCV] Add a test of vector sadd.overflow to demonstrate intrinsics with multiple scalable vector results."

This reverts commit 2c51bef76cbf0149101b9e7c7c658b4a58657929.

I seem to have messed up the check lines in the test.

Recommit "[RISCV] Add a test of vector sadd.overflow to demonstrate intrinsics with multiple scalable vector results."

This recommits 2c51bef76cbf0149101b9e7c7c658b4a58657929.

I've fixed the broken check line from when I renamed the test function.

Original commit message:
This builds on D94142 where scalable vectors are allowed in structs.

I did have to fix one scalable vector issue in the vector type
creation for these intrinsics where we used getVectorNumElements
instead of ElementCount.

[libc++] Rename check-cxx-deps to cxx-test-depends for consistency

Several subprojects have targets that do the same thing, and they all
follow the same naming convention: llvm-test-depends, clang-test-depends,
lld-test-depends, etc.

This makes libc++ consistent with other LLVM projects.
Thanks to Duncan Exon Smith for noticing and suggesting the change.

Differential Revision: https://reviews.llvm.org/D94499

[NFC] Update some mlir python documentation.

* Development setup recommendations.
* Test updates to match what we actually do.
* Update cmake variable `PYTHON_EXECUTABLE` -> `Python3_EXECUTABLE` to match the upgrade to python3 repo wide.

[libc++] improve feature test macro script

I've been playing a bit with the `generate_feature_test_macro_components.py` script and replaced some hardcoded values with extra code generation (generate ALL the things).
The output is the same and it makes updating the script less work for the coming 25 C++ standards (until 2 digit number overflow).

Feel free to 'veto' if you think it's overkill.

Differential Revision: https://reviews.llvm.org/D94530

NFC: Document current MLIR Python ODS conventions.

* We had let the documentation get stale and catching it up prior to proposing changes.