workflows: Use sccache to speed up CI builds

Reviewed By: asl

Differential Revision: https://reviews.llvm.org/D129880

.github/workflows/llvm-project-tests.yml

@@ -50,9 +50,25 @@ jobs:
           arch: amd64
       - name: Install Ninja
         uses: llvm/actions/install-ninja@main
+      # actions/checkout deletes any existing files in the new git directory,
+      # so this needs to either run before ccache-action or it has to use
+      # clean: false.
       - uses: actions/checkout@v3
         with:
           fetch-depth: 250
+      - name: Setup ccache
+        uses: hendrikmuhs/ccache-action@v1.2
+        with:
+          # A full build of llvm, clang, lld, and lldb takes about 250MB
+          # of ccache space. There's not much reason to have more than this,
+          # because we usually won't need to save cache entries from older
+          # builds.  Also, there is an overall 10GB cache limit, and each
+          # run creates a new cache entry so we want to ensure that we have
+          # enough cache space for all the tests to run at once and still
+          # fit under the 10 GB limit.
+          max-size: 500M
+          key: sccache-${{ matrix.os }}
+          variant: sccache
       - name: Build and Test
         uses: llvm/actions/build-test-llvm-project@main
         env:
@@ -60,7 +76,7 @@ jobs:
           # This should be a no-op for non-mac OSes
           PKG_CONFIG_PATH: /usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig//11
         with:
-          cmake_args: '-GNinja -DLLVM_ENABLE_PROJECTS="${{ inputs.projects }}" -DCMAKE_BUILD_TYPE=Release -DLLDB_INCLUDE_TESTS=OFF'
+          cmake_args: '-GNinja -DLLVM_ENABLE_PROJECTS="${{ inputs.projects }}" -DCMAKE_BUILD_TYPE=Release -DLLDB_INCLUDE_TESTS=OFF -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache'
           build_target:  '${{ inputs.build_target }}'
 
       - name: Build and Test libclc