Try older clang on focal.

.github/workflows/ci.yml

@@ -146,6 +146,50 @@ jobs:
       - name: Test
         run: ../../../b2 toolset=$TOOLSET cxxstd=03,11,14,17,2a
         working-directory: ../boost-root/libs/config/test
+  ubuntu-focal-clang:
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+      matrix:
+        compiler: [ clang++-11, clang++-12, clang++-13, clang++-14 ]
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: '0'
+      - uses: mstachniuk/ci-skip@v1
+        with:
+          commit-filter: '[skip ci];[ci skip];[CI SKIP];[SKIP CI];***CI SKIP***;***SKIP CI***;[windows];[Windows];[WINDOWS];[apple];[Apple];[APPLE]'
+          commit-filter-separator: ';'
+          fail-fast: true
+      - name: Set TOOLSET
+        run: echo ${{ matrix.compiler }} | awk '/^g/ { print "TOOLSET=gcc" } /^clang/ { print "TOOLSET=clang" }' >> $GITHUB_ENV
+      - name: Add repository
+        run: sudo apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
+      - name: Install packages
+        run: sudo apt install clang-11 clang-12 clang-13 clang-14
+      - name: Checkout main boost
+        run: git clone -b develop --depth 1 https://github.com/boostorg/boost.git ../boost-root
+      - name: Update Dependencies
+        run: git submodule update --init tools/build tools/boost_install libs/headers libs/detail libs/core libs/assert libs/type_traits
+        working-directory: ../boost-root
+      - name: Copy files
+        run: cp -r $GITHUB_WORKSPACE/* libs/config
+        working-directory: ../boost-root
+      - name: Bootstrap
+        run: ./bootstrap.sh
+        working-directory: ../boost-root
+      - name: Generate headers
+        run: ./b2 headers
+        working-directory: ../boost-root
+      - name: Generate user config
+        run: 'echo "using $TOOLSET : : ${{ matrix.compiler }} ;" > ~/user-config.jam'
+        working-directory: ../boost-root
+      - name: Config info
+        run: ../../../b2 print_config_info toolset=$TOOLSET cxxstd=03,11,14,17,2a
+        working-directory: ../boost-root/libs/config/test
+      - name: Test
+        run: ../../../b2 toolset=$TOOLSET cxxstd=03,11,14,17,2a
+        working-directory: ../boost-root/libs/config/test
   macos_11:
     runs-on: macos-11
     strategy: