[CI] Make premerge upload/write comments

.ci/premerge_advisor_explain.py

@@ -39,6 +39,7 @@ def get_comment(
 ) -> dict[str, str]:
     repo = github.Github(github_token).get_repo("llvm/llvm-project")
     pr = repo.get_issue(pr_number).as_pull_request()
+    body = COMMENT_TAG.format(platform=platform.system()) + "\n" + body
     comment = {"body": body}
     comment_id = get_comment_id(platform.system(), pr)
     if comment_id:
@@ -128,7 +129,7 @@ def main(
                 ),
             )
         ]
-        with open("comment", "w") as comment_file_handle:
+        with open("comments", "w") as comment_file_handle:
             json.dump(comments, comment_file_handle)
     else:
         print(advisor_response.reason)

.github/workflows/premerge.yaml

@@ -119,6 +119,14 @@ jobs:
           path: artifacts/
           retention-days: 5
           include-hidden-files: 'true'
+      - name: Upload Comment
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        if: ${{ always() && !startsWith(matrix.runs-on, 'depot-ubuntu-24.04-arm') }}
+        continue-on-error: true
+        with:
+          name: workflow-args
+          path: |
+            comments
 
   premerge-checks-windows:
     name: Build and Test Windows