[llvm] [CI] Add Github actions job to build LLVM documentation (PR #69269)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/69269

This patch adds in support for building the LLVM documentation through a Github actions job. This enables catching documentation build failures earlier and also more easily as the job failure will show up directly on pull requests. The job currently only builds the documentation for LLVM, but the plan is to extend it to also build the documentation for other subprojects when appropriate (i.e., the docs files have changed), starting with clang.

>From 63bb10129164e9b22b4ce626aaaacd0b45132418 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <agrossman154 at yahoo.com>
Date: Mon, 16 Oct 2023 17:52:04 -0700
Subject: [PATCH] [CI] Add Github actions job to build LLVM documentation

---
 .github/workflows/docs.yml | 43 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 .github/workflows/docs.yml

diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
new file mode 100644
index 000000000000000..d00cfab0ff28671
--- /dev/null
+++ b/.github/workflows/docs.yml
@@ -0,0 +1,43 @@
+# LLVM Documentation CI
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+name: "Test documentation build"
+
+on:
+  push:
+    branches:
+      - 'main'
+    paths:
+      - 'llvm/docs/**'
+  pull_request:
+    paths:
+      - 'llvm/docs/**'
+
+jobs:
+  check-docs-build:
+    name: "Test documentation build"
+    runs-on: ubuntu-latest
+    steps:
+      - name: Fetch LLVM sources
+        uses: actions/checkout at v4
+        with:
+          fetch-depth: 2
+      - name: Setup Python env
+        uses: actions/setup-python at v4
+        with:
+          python-version: '3.11'
+          cache: 'pip'
+          cache-dependency-path: 'llvm/docs/requirements.txt'
+      - name: Install python dependencies
+        run: pip install -r llvm/docs/requirements.txt
+      - name: Install system dependencies
+        run: apt-get update && apt-get install -y cmake ninja-build
+      - name: Build docs
+        run: |
+          mkdir build
+          cd build
+          cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_SPHINX=ON -DSPHINX_OUTPUT_HTML=ON -DSPHINX_OUTPUT_MAN=ON ../llvm
+          TZ=UTC ninja docs-llvm-html docs-llvm-man
+