Fix cache_dir path for ccache config (#8370)

Previously we are missing `ccache --set-config=cache_dir="$ccache_dir"`
and the build was using the default cache_dir.
This PR fixed that and the cache are hit in reruns.

```
📊 ccache statistics (post-build):
Cacheable calls:    1198 / 1198 (100.0%)
  Hits:             1195 / 1198 (99.75%)
    Direct:         1193 / 1195 (99.83%)
    Preprocessed:      2 / 1195 ( 0.17%)
  Misses:              3 / 1198 ( 0.25%)
Local storage:
  Cache size (GiB):  0.6 /  5.0 (11.11%)
  Hits:             1195 / 1198 (99.75%)
  Misses:              3 / 1198 ( 0.25%)
```

1 files changed, 8 insertions, 9 deletions

diff --git a/.github/actions/common-setup/action.yml b/.github/actions/common-setup/action.yml
index 1ab2d1a48..5f4bac02c 100644
--- a/.github/actions/common-setup/action.yml
+++ b/.github/actions/common-setup/action.yml
@@ -150,26 +150,25 @@ runs:
         echo "✅ ccache found on self-hosted runner - setting up persistent caching"
 
         # Set ccache directory to a persistent location outside workspace
-        # Use runner temp directory with a unique path per repo/compiler/platform
-        ccache_base_dir="${RUNNER_TEMP:-/tmp}/ccache-slang"
+        if [[ "${{ inputs.os }}" == "windows" ]]; then
+          ccache_base_dir="C:/ccache-slang"
+        else
+          # Linux/macOS: Use home directory for persistence
+          ccache_base_dir="$HOME/.ccache-slang"
+        fi
         ccache_dir="$ccache_base_dir/${{ inputs.os }}-${{ inputs.compiler }}-${{ inputs.platform }}"
         mkdir -p "$ccache_dir"
         echo "CCACHE_DIR=$ccache_dir" >> $GITHUB_ENV
         echo "🔧 Using persistent ccache directory: $ccache_dir"
 
         # Configure ccache settings for local use only
-        ccache --set-config=max_size=2G
+        ccache --set-config=max_size=20G
         ccache --set-config=compression=true
         ccache --set-config=compression_level=6
         ccache --set-config=sloppiness=pch_defines,time_macros
+        ccache --set-config=cache_dir="$ccache_dir"
 
         # Enable ccache for CMake (set environment variables)
         # Get the full path to ccache executable
         ccache_path=$(which ccache)
         echo "ccache_symlinks_path=$ccache_path" >> $GITHUB_ENV
-
-        # Show initial stats
-        echo "ccache configuration:"
-        ccache --show-config || echo "Could not show ccache config"
-        ccache --zero-stats || echo "Could not zero ccache stats"
-        ccache --show-stats || echo "Could not show ccache stats"