[CI] Enable sccache GCS on Linux premerge (llvm#149923)

This patch enables sccache using GCS for Linux premerge.

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -34,11 +34,6 @@ jobs:
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           fetch-depth: 2
-      - name: Setup ccache
-        uses: hendrikmuhs/ccache-action@a1209f81afb8c005c13b4296c32e363431bffea5 # v1.2.17
-        with:
-          variant: "sccache"
-          max-size: "2000M"
       - name: Build and Test
         # Mark the job as a success even if the step fails so that people do
         # not get notified while the new premerge pipeline is in an
@@ -62,6 +57,13 @@ jobs:
           export CC=/opt/llvm/bin/clang
           export CXX=/opt/llvm/bin/clang++
 
+          # This environment variable is passes into the container through the
+          # runner pod definition. This differs between our two clusters which
+          # why we do not hardcode it.
+          export SCCACHE_GCS_BUCKET=$CACHE_GCS_BUCKET
+          export SCCACHE_GCS_RW_MODE=READ_WRITE
+          sccache --start-server
+
           ./.ci/monolithic-linux.sh "${projects_to_build}" "${project_check_targets}" "${runtimes_to_build}" "${runtimes_check_targets}" "${runtimes_check_targets_needs_reconfig}" "${enable_cir}"
       - name: Upload Artifacts
         if: '!cancelled()'

polly/CMakeLists.txt

@@ -1,3 +1,4 @@
+# test
 # Check if this is a in tree build.
 if (NOT DEFINED LLVM_MAIN_SRC_DIR)
   project(Polly)