ci: Add a clang-ast workflow

This does compile time type-checking using a clang-plugin. It was run as
part of buildbot.

Link: <https://github.com/ac000/clang-ast/tree/unit-stdc%2B%2B17>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

.github/workflows/clang-ast.yaml

@@ -0,0 +1,51 @@
+name: "Clang AST"
+
+on:
+  push:
+    branches: master
+    paths:
+      - configure
+      - 'auto/**'
+      - 'src/**'
+      - 'test/**'
+      - '.github/workflows/clang-ast.yaml'
+  pull_request:
+    branches: master
+    paths:
+      - configure
+      - 'auto/**'
+      - 'src/**'
+      - 'test/**'
+      - '.github/workflows/clang-ast.yaml'
+
+jobs:
+  clang-ast:
+    runs-on: ubuntu-latest
+
+    container:
+      image: debian:testing
+
+    steps:
+      - name: Install tools/deps
+        run: |
+          apt-get -y update
+          apt-get -y install git llvm-dev libclang-dev clang make \
+                             libssl-dev libpcre2-dev
+
+      - uses: actions/checkout@v4
+
+      - name: Checkout and build clang-ast
+        run: |
+          git clone https://github.com/nginx/clang-ast.git -b unit
+          cd clang-ast
+          make
+
+      - name: Configure Unit
+        run: ./configure --cc=clang --cc-opt="-Xclang -load -Xclang clang-ast/ngx-ast.so -Xclang -add-plugin -Xclang ngx-ast" --openssl --debug --tests
+
+      - name: Build Unit
+        run: |
+          make -j4 NXT_SHARED_LOCAL_LINK=: build/lib/libnxt.so
+
+      - name: Build C tests
+        run: make -j4 tests