From 17ca29775b5cd17ca1e0ba8e9628e5244b2eaaa9 Mon Sep 17 00:00:00 2001
From: Brandon Ros <brandonros1@gmail.com>
Date: Mon, 21 Sep 2026 09:44:31 -0400
Subject: [PATCH] Upgrade modern backend to LLVM 21.1.8 and CUDA 13.3

Replace the LLVM 19 backend feature with LLVM 21 while retaining LLVM 7
for the legacy path. Update feature forwarding, LLVM tool discovery, the
vector-add example, the Nix shell, container definitions, and docs.

- rustc_llvm_wrapper: guard the Instrumentation.h include to LLVM < 19 and
  update wrapper APIs for LLVM 21; add tests/llvm-wrapper capture checks.
- nvvm: restore kernel annotations after the LLVM 21 bitcode upgrade.
- cust: handle CUDA 13.3's CU_GRAPH_NODE_TYPE_RESERVED_16 graph node type.
- CI: add LLVM 21 vector-add jobs on x86_64 and aarch64 using CUDA 13.3.1
  and LLVM 21.1.8 prebuilts, with a configurable PREBUILT_LLVM_URL; install
  libzstd-dev so the static LLVM link resolves -lzstd.
- Update the Windows CUDA installer action for CUDA 13.3.1.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>