ci: statically link libc

Move configuration values to the matrix action and statically links both `libgcc` and `libstdc++`.

Since we are using the latest version of ubuntu in our workflow, this is intended to allow the release binaries to work on any earlier version of ubuntu. This is required by the Antora scripts in the Boost release tools.

Author: alandefreitas

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
 
     name: ${{ matrix.name }}
     runs-on: ${{ matrix.runs-on }}
-    container: ${{ (matrix.compiler == 'gcc' && 'ubuntu:22.04') || matrix.container }}
+    container: ${{ matrix.container }}
     env: ${{ matrix.env }}
     permissions:
       contents: write
@@ -86,6 +86,7 @@ jobs:
           ccflags: ${{ matrix.ccflags }}
           cxx: ${{ steps.setup-cpp.outputs.cxx || matrix.cxx }}
           cxxflags: ${{ matrix.cxxflags }}
+          vcpkg-triplet: ${{ matrix.compiler == 'gcc' && 'x64-linux-static' || '' }}
 
       - name: Install LLVM
         id: llvm-install
@@ -137,9 +138,9 @@ jobs:
           cmake-version: '>=3.20'
           cxxstd: ${{ matrix.cxxstd }}
           cc: ${{ steps.setup-cpp.outputs.cc || matrix.cc }}
-          ccflags: ${{ matrix.ccflags }}
+          ccflags: ${{ matrix.cxxflags }}${{ ( matrix.compiler == 'gcc' && ' -static -static-libgcc -static-libstdc++ -static-libstdc++') || '' }}${{ ( matrix.asan && ' -static-libasan') || '' }}${{ ( matrix.tsan && ' -static-libtsan') || '' }}
           cxx: ${{ steps.setup-cpp.outputs.cxx || matrix.cxx }}
-          cxxflags: ${{ matrix.cxxflags }}${{ ( matrix.compiler == 'gcc' && ' -static-libstdc++') || '' }}${{ ( matrix.asan && ' -static-libasan') || '' }}${{ ( matrix.tsan && ' -static-libtsan') || '' }}
+          cxxflags: ${{ matrix.cxxflags }}${{ ( matrix.compiler == 'gcc' && ' -static -static-libgcc -static-libstdc++ -static-libstdc++') || '' }}${{ ( matrix.asan && ' -static-libasan') || '' }}${{ ( matrix.tsan && ' -static-libtsan') || '' }}
           generator: Ninja
           toolchain: ${{ steps.package-install.outputs.vcpkg_toolchain || steps.package-install.outputs.vcpkg-toolchain }}
           build-type: ${{ matrix.build-type }}
@@ -155,6 +156,8 @@ jobs:
           package-generators: ${{ (runner.os == 'Windows' && '7Z ZIP WIX') || 'TGZ TXZ' }}
           package-artifact: false
 
+      # The artifacts will be downloaded in the next jobs to
+      # create the releases.
       - name: Upload GitHub Release Artifacts
         if: ${{ matrix.is-main && matrix.compiler != 'clang' }}
         uses: actions/upload-artifact@v3
@@ -171,7 +174,7 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Codecov
-        if: ${{ matrix.coverage}}
+        if: ${{ matrix.coverage }}
         uses: codecov/codecov-action@v3.1.4
         with:
           directory: './build'
@@ -248,8 +251,9 @@ jobs:
 
     name: Demos
     timeout-minutes: 120
+    # We run the demos with ubuntu-22.04 to ensure
+    # the binary works on earlier versions of ubuntu.
     runs-on: ubuntu-22.04
-    container: ubuntu:23.04
 
     permissions:
       contents: write
@@ -297,6 +301,9 @@ jobs:
           modules-exclude-paths: ''
           trace-commands: true
 
+      # Boost.URL has its own mrdocs.yml file. We go through the
+      # multi/single and adoc/html/xml formats and patch the
+      # mrdocs.yml file for each combination.
       - name: Generate demos
         run: |
           set -x
@@ -319,13 +326,15 @@ jobs:
           tar -cjf $(pwd)/demos.tar.gz -C $(pwd)/demos --strip-components 1 .
           echo "demos_path=$(pwd)/demos.tar.gz" >> $GITHUB_ENV
 
+      # Upload the demos as artifacts, so we can see them in PRs.
       - name: Upload demo artifacts
         uses: actions/upload-artifact@v3
         with:
           name: demos
           path: ${{ env.demos_path }}
           retention-days: 1
 
+      # Upload the demos to the website when pushing to master, develop, or creating a tag.
       - name: Update website demos
         if: ${{ github.event_name == 'push' && (contains(fromJSON('["master", "develop"]'), github.ref_name) || startsWith(github.ref, 'refs/tags/')) }}
         env:
@@ -345,6 +354,10 @@ jobs:
           chmod 755 -R $(pwd)/demos
           scp -r $(pwd)/demos/* ubuntu@dev-websites.cpp.al:$demo_dir/
 
+  # Create releases after being able to build the demos.
+  # When the releases overwrite the `master` or `develop` releases,
+  # GitHub might attempt to create a draft release which needs to
+  # be converted to a regular release manually.
   releases:
     needs: build
     defaults: