Use C++20 (#6877)

.github/workflows/osrm-backend.yml

@@ -396,7 +396,36 @@ jobs:
         elif [[ "${RUNNER_OS}" == "macOS" ]]; then
           echo "JOBS=$((`sysctl -n hw.ncpu` + 1))" >>  $GITHUB_ENV
         fi
+    # See: https://github.com/actions/toolkit/issues/946#issuecomment-1590016041
+    # We need it to be able to access system folders while restoring cached Boost below
+    - name: Give tar root ownership 
+      if: runner.os == 'Linux' && matrix.ENABLE_CONAN != 'ON'
+      run: sudo chown root /bin/tar && sudo chmod u+s /bin/tar
+    - name: Cache Boost
+      if: runner.os == 'Linux' && matrix.ENABLE_CONAN != 'ON'
+      id: cache-boost
+      uses: actions/cache@v4
+      with:
+        path: |
+          /usr/local/include/boost
+          /usr/local/lib/libboost*
+        key: v1-boost-${{ runner.os }}-${{ runner.arch }}-${{ matrix.runs-on }}
+        restore-keys: |
+          v1-boost-${{ runner.os }}-${{ runner.arch }}-${{ matrix.runs-on }}
 
+    - name: Install Boost
+      if: steps.cache-boost.outputs.cache-hit != 'true' && runner.os == 'Linux' && matrix.ENABLE_CONAN != 'ON'
+      run: |
+        BOOST_VERSION="1.85.0"
+        BOOST_VERSION_UNDERSCORE="${BOOST_VERSION//./_}"
+        wget -q https://boostorg.jfrog.io/artifactory/main/release/${BOOST_VERSION}/source/boost_${BOOST_VERSION_UNDERSCORE}.tar.gz
+        tar xzf boost_${BOOST_VERSION_UNDERSCORE}.tar.gz
+        cd boost_${BOOST_VERSION_UNDERSCORE}
+        sudo ./bootstrap.sh
+        sudo ./b2 install
+        cd ..
+        sudo rm -rf boost_${BOOST_VERSION_UNDERSCORE}*
+    
     - name: Install dev dependencies
       run: |
         python3 -m pip install "conan<2.0.0" || python3 -m pip install "conan<2.0.0" --break-system-packages
@@ -417,7 +446,7 @@ jobs:
         # Linux dev packages
         if [ "${ENABLE_CONAN}" != "ON" ]; then
           sudo apt-get update -y
-          sudo apt-get install -y libbz2-dev libxml2-dev libzip-dev liblua5.2-dev libboost-all-dev
+          sudo apt-get install -y libbz2-dev libxml2-dev libzip-dev liblua5.2-dev
           if [[ "${CCOMPILER}" != clang-* ]]; then
             sudo apt-get install -y ${CXXCOMPILER}
           fi