[llvm] [Github] Add support for building libc docs in Github actions (PR #69824)

[via llvm-commits]

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@@ -69,4 +73,10 @@ jobs:
         run: |
           cmake -B clang-build -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_SPHINX=ON ./llvm
           TZ=UTC ninja -C clang-build docs-clang-html docs-clang-man
+      - name: Build libc docs
+        if: steps.docs-changed-subprojects.outputs.libc_any_changed == 'true'
+        run: |
+          cmake -B libc-build -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RUNTIMES="libc" -DLLVM_ENABLE_SPHINX=ON ./runtimes
+          TZ=UTC ninja -C libc-build docs-libc-html
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michaelrj-google wrote:

`libc-build` isn't the target for building LLVM libc. The target is just `libc`.

https://github.com/llvm/llvm-project/pull/69824