GHA: Cache built gdb executable

Author: kinke

.github/actions/helper-build-gdb/action.yml

@@ -0,0 +1,38 @@
+name: Build gdb from source
+inputs:
+  arch:
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Try to restore cached gdb executable
+      uses: actions/cache@v4
+      with:
+        path: /usr/local/bin/gdb
+        key: gdb-${{ inputs.arch }}
+
+    - shell: bash
+      run: |
+        set -eux
+
+        if [[ -f /usr/local/bin/gdb ]]; then
+          echo "Already cached"
+          exit 0
+        fi
+
+        sudo apt-get -yq install libmpfr-dev
+
+        cd ..
+        curl -fL --retry 3 --max-time 60 -O https://mirrors.ocf.berkeley.edu/gnu/gdb/gdb-16.2.tar.xz
+        tar xf gdb-16.2.tar.xz
+
+        cd gdb-16.2
+        ./configure
+        make -j$(nproc)
+        sudo make install
+        cd ..
+
+        rm -rf gdb-16.2 gdb-16.2.tar.xz
+
+    - shell: bash
+      run: gdb --version

.github/workflows/main.yml

@@ -153,19 +153,9 @@ jobs:
           arch: ${{ matrix.arch }}
       - name: 'Ubuntu 22: Build recent gdb from source' # see https://github.com/ldc-developers/ldc/issues/4389
         if: startsWith(matrix.os, 'ubuntu-22.04')
-        run: |
-          set -eux
-          cd ..
-          sudo apt-get -yq install libmpfr-dev
-          curl -fL --retry 3 --max-time 60 -O https://mirrors.ocf.berkeley.edu/gnu/gdb/gdb-16.2.tar.xz
-          tar xf gdb-16.2.tar.xz
-          cd gdb-16.2
-          ./configure
-          make -j$(nproc)
-          sudo make install
-          cd ..
-          rm -rf gdb-16.2 gdb-16.2.tar.xz
-          gdb --version
+        uses: ./.github/actions/helper-build-gdb
+        with:
+          arch: ${{ matrix.arch }}
       - name: Build bootstrap LDC
         if: runner.os != 'macOS'
         uses: ./.github/actions/2-build-bootstrap