add workflow to build with all available C standards

.github/workflows/c-std.yml

@@ -0,0 +1,104 @@
+name: C Standard
+
+on:
+  workflow_dispatch:
+  push:
+  pull_request:
+
+jobs:
+  configure:
+    name: ${{ matrix.compiler }} + ${{ matrix.builder }} -std=${{ matrix.std }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+
+        compiler:
+          - gcc
+          - clang
+
+        builder:
+          - configure
+          - cmake
+
+        std:
+          - c89
+          - gnu89
+          # c94 is iso9899:199409 for both gcc & clang
+          - iso9899:199409
+          - c99
+          - gnu99
+          - c11
+          - gnu11
+          - c17
+          - gnu17
+          - c2x
+          - gnu2x
+
+    steps:
+
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        show-progress: 'false'
+
+    - name: Install packages (Ubuntu)
+      run: |
+        sudo apt-get update
+
+    - name: Generate project files (configure)
+      if: matrix.builder == 'configure'
+      run: |
+        ./configure
+      env:
+        CC: ${{ matrix.compiler }}
+        CFLAGS: -std=${{ matrix.std }} -Werror
+
+    - name: Compile source code (configure)
+      if: matrix.builder == 'configure'
+      run: make -j2
+
+    - name: Run test cases (configure)
+      if: matrix.builder == 'configure'
+      run: |
+        make test
+        make cover
+
+    - name: Generate project files (cmake)
+      if: matrix.builder == 'cmake'
+      run: |
+        cmake -S . -B . -D CMAKE_BUILD_TYPE=Release -D ZLIB_BUILD_EXAMPLES=OFF
+      env:
+        CC: ${{ matrix.compiler }}
+        CFLAGS: -std=${{ matrix.std }} -Werror
+
+    - name: Compile source code (cmake)
+      if: matrix.builder == 'cmake'
+      run: cmake --build . --config Release
+
+    - name: Run test cases (cmake)
+      if: matrix.builder == 'cmake'
+      run: ctest -C Release --output-on-failure --max-width 120
+
+    - name: Upload build errors (configure)
+      uses: actions/upload-artifact@v4
+      if: failure() && matrix.builder == 'configure'
+      with:
+        name: ${{ matrix.compiler }} ${{ matrix.std }} (configure)
+        path: |
+          ./configure.log
+        if-no-files-found: ignore
+        retention-days: 7
+
+    - name: Upload build errors (cmake)
+      uses: actions/upload-artifact@v4
+      if: failure() && matrix.builder == 'cmake'
+      with:
+        name: ${{ matrix.compiler }} ${{ matrix.std }} (cmake)
+        path: |
+          **/CMakeFiles/CMakeOutput.log
+          **/CMakeFiles/CMakeError.log
+        if-no-files-found: ignore
+        retention-days: 7