Apply LLVM patches for deterministic operand order and correct peephole optimization for minsize (#500)

## Description

Applies LLVM patches that have not been backported to the major version
used in our submodule:

* [LLVM PR #163679](https://github.com/llvm/llvm-project/pull/163679)
  * *"[RISCV] Allow large div peephole optimization for minsize"*
* Fixes peephole optimization of large integers when `minsize` function
attribute is set.
* (Our revive codebase used a workaround that can be removed once this
500 PR is merged and we publish a new LLVM release.)
* [LLVM PR #190219](https://github.com/llvm/llvm-project/pull/190219)
* *"[TargetLowering] Speculative fix for a non-determinism issue between
different compilers"*
* Operand ordering of `mul i256` were different depending on the target
ABI when building LLVM, producing different RISC-V and PVM bytecode for
our Windows vs macOS/linux builds.
* The bytecode divergence (yet functionally equivalent) affected
Solidity contracts containing a value [multiplied by
itself](https://github.com/llvm/llvm-project/issues/190148) (e.g. via
explicit squaring or exponentiation), manifesting primarily when using
optimization level `-O0`.

.github/actions/get-llvm/action.yml

@@ -8,7 +8,7 @@ inputs:
   target:
     required: true
   version:
-    description: "LLVM release version (e.g., 'llvm-18.1.8'). If not specified, uses the latest LLVM release."
+    description: "LLVM release version (e.g., 'llvm-18.1.8'). If not specified, uses the latest published LLVM release. To test a specific draft release, use the full name (e.g. 'llvm-21.1.8-revive.0f80912')."
     required: false
     default: ""
 
@@ -114,7 +114,9 @@ runs:
               core.setFailed(`Artifact for '${target}' not found in release ${llvmRelease.tag_name} (${llvmRelease.html_url})`);
               process.exit();
             }
-            return asset.browser_download_url;
+            // Use the API URL (rather than `browser_download_url`) so that
+            // the authorization header is respected for draft releases.
+            return asset.url;
           }
 
           if (versionPrefix) {
@@ -127,7 +129,8 @@ runs:
     - name: download
       shell: bash
       run: |
-        curl -sSLo llvm.tar.gz ${{ steps.find.outputs.result }}
+        # Pass the authorization token to allow downloading draft release assets.
+        curl -sSLo llvm.tar.gz -H "Authorization: Bearer ${{ github.token }}" -H "Accept: application/octet-stream" ${{ steps.find.outputs.result }}
 
     - name: unpack
       shell: bash