GH Actions: ccache on macOS & Linux; sccache on Windows

Signed-off-by: Be <be@mixxx.org>

.github/workflows/cmake_build.yml

@@ -35,11 +35,15 @@ jobs:
           os: ubuntu-18.04
           arch: x86_64 # as reported by `arch` or `uname -m`
           generator: Unix Makefiles
+          compiler_cache: ccache
+          compiler_cache_path: ~/.ccache
 
         - name: macOS_Intel
           os: macos-latest
           arch: Intel # as reported by Apple menu > About This Mac
           generator: Unix Makefiles
+          compiler_cache: ccache
+          compiler_cache_path: ~/Library/Caches/ccache
 
         - name: Windows_32bit
           os: windows-latest
@@ -48,6 +52,8 @@ jobs:
           cc: cl
           cxx: cl
           generator: Ninja
+          compiler_cache: sccache
+          compiler_cache_path: C:\Users\runneradmin\AppData\Local\Mozilla\sccache\cache
 
         - name: Windows_64bit
           os: windows-latest
@@ -56,6 +62,8 @@ jobs:
           cc: cl
           cxx: cl
           generator: Ninja
+          compiler_cache: sccache
+          compiler_cache_path: C:\Users\runneradmin\AppData\Local\Mozilla\sccache\cache
 
     steps:
 
@@ -73,7 +81,7 @@ jobs:
     - name: Install Apple codesigning certificates
       uses: apple-actions/import-codesign-certs@v1
       if: startswith( matrix.config.os, 'macos' ) && github.event_name == 'push' && github.repository_owner == 'audacity'
-      with: 
+      with:
         p12-file-base64: ${{ secrets.APPLE_CERTIFICATE }}
         p12-password: ${{ secrets.APPLE_CERTIFICATE_PASSWORD }}
 
@@ -84,6 +92,19 @@ jobs:
       with:
         arch: ${{ matrix.config.arch }}
 
+    - name: "[Windows] Install sccache"
+      if: runner.os == 'Windows'
+      run: choco install sccache
+
+    - name: "Set up compiler cache"
+      uses: actions/cache@v2
+      with:
+        path: ${{ matrix.config.compiler_cache_path }}
+        key: ${{ matrix.config.os }}-${{ matrix.config.arch }}-${{ github.head_ref }}-${{ github.run_number }}
+        restore-keys: |
+          ${{ matrix.config.os }}-${{ matrix.config.arch }}-${{ github.head_ref }}-
+          ${{ matrix.config.os }}-${{ matrix.config.arch }}-
+
     - name: Cache for .conan
       id: cache-conan
       uses: actions/cache@v2
@@ -110,6 +131,9 @@ jobs:
       run: |
         exec bash "scripts/ci/build.sh"
 
+    - name: "Print compiler cache stats"
+      run: ${{ matrix.config.compiler_cache }} -s
+
     - name: Install
       run: |
         exec bash "scripts/ci/install.sh"