[llvm] [Github] Add steps to build clang docs to CI (PR #69550)

[Tom Stellard via llvm-commits]

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@@ -39,10 +41,27 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y cmake ninja-build
-      - name: Build docs
+      - name: Get subprojects that have doc changes
+        id: docs-changed-subprojects
+        uses: tj-actions/changed-files at v39
+        with:
+          files_yaml: |
+            llvm:
+              - 'llvm/docs/**'
+            clang:
+              - 'clang/docs/**'
+      - name: Build LLVM docs
+        if: steps.docs-changed-subprojects.outputs.llvm_any_changed == 'true'
         run: |
-          mkdir build
-          cd build
+          mkdir llvm-build
+          cd llvm-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
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tstellar wrote:

And then pass `-C llvm-build ` here.

https://github.com/llvm/llvm-project/pull/69550