ci: Dump deprecated Ubuntu 20.04 runner

Ubuntu 20.04 runners for GitHub Actions have been retired. Let's remove
them from the build matrix, to avoid failures in our CI.

We want to add Ubuntu 24.04 instead, but need to finalise
#179 for that.

Link: https://github.blog/changelog/2025-01-15-github-actions-ubuntu-20-runner-image-brownout-dates-and-other-breaking-changes/
Signed-off-by: Quentin Monnet <[email protected]>

Author: qmonnet

.github/workflows/build.yaml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, ubuntu-22.04]
+        os: [ubuntu-22.04, macos-14]
     runs-on: ${{ matrix.os }}
     env:
       FEATURES: .llvm and .skeletons
@@ -32,13 +32,8 @@ jobs:
         with:
           submodules: true
 
-      - name: Use clang-12 and not clang-11 for older Ubuntu
-        if: matrix.os == 'ubuntu-20.04'
-        run: |
-          sudo apt-get remove -y clang-11 llvm-11
-          sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-12 50
-
-      - name: Install dependencies
+      - name: Install dependencies (Linux)
+        if: startsWith(matrix.os, 'ubuntu')
         run: |
           sudo apt-get update
           sudo apt-get install -y \
@@ -51,6 +46,33 @@ jobs:
               --slave /usr/bin/llvm-strip llvm-strip /usr/bin/llvm-strip-"${CLANG_VERSION}"
           echo "CLANG_VERSION=${CLANG_VERSION}" >> "${GITHUB_ENV}"
 
+      - name: Install dependencies (macOS)
+        if: startsWith(matrix.os, 'macos')
+        run: |
+          brew update
+          brew install \
+              binutils \
+              libelf \
+              docutils \
+              jq \
+              llvm
+
+          # Set up LLVM paths and aliases
+          LLVM_PATH="$(brew --prefix llvm)"
+          CLANG_VERSION="$(echo '__clang_major__' | ${LLVM_PATH}/bin/clang -E - | tail -n 1)"
+
+          # Create symlinks for LLVM tools in a directory that's in PATH
+          mkdir -p "${HOME}/bin"
+          ln -sf "${LLVM_PATH}/bin/llvm-config" "${HOME}/bin/llvm-config"
+          ln -sf "${LLVM_PATH}/bin/llvm-ar" "${HOME}/bin/llvm-ar"
+          ln -sf "${LLVM_PATH}/bin/llvm-strip" "${HOME}/bin/llvm-strip"
+          ln -sf "${LLVM_PATH}/bin/clang" "${HOME}/bin/clang"
+
+          # Add to PATH
+          echo "${HOME}/bin" >> $GITHUB_PATH
+          echo "CLANG_VERSION=${CLANG_VERSION}" >> "${GITHUB_ENV}"
+          echo "LLVM_PATH=${LLVM_PATH}" >> "${GITHUB_ENV}"
+
       - name: Build bpftool (default LLVM disassembler)
         run: |
           make -j -C src V=1
@@ -68,7 +90,8 @@ jobs:
               tee /dev/stderr | \
               jq --exit-status ".features | ${FEATURES}"
 
-      - name: Build bpftool, with fallback to libbfd disassembler
+      - name: Build bpftool, with fallback to libbfd disassembler (Linux)
+        if: startsWith(matrix.os, 'ubuntu')
         run: |
           sudo apt-get remove -y llvm-"${CLANG_VERSION}"-dev
           make -C src clean
@@ -78,7 +101,8 @@ jobs:
               tee /dev/stderr | \
               jq --exit-status ".features | .libbfd and (.llvm | not)"
 
-      - name: Build bpftool, with libbfd, static build
+      - name: Build bpftool, with libbfd, static build (Linux)
+        if: startsWith(matrix.os, 'ubuntu')
         run: |
           make -C src clean
           EXTRA_CFLAGS=--static make -j -C src V=1