[llvm] Depot runners arm (PR #120786)

[Carlo Cabrera via llvm-commits]

================
@@ -120,8 +124,21 @@ jobs:
 
         # Detect necessary CMake flags
         target="${{ runner.os }}-${{ runner.arch }}"
-        echo "enable-pgo=false" >> $GITHUB_OUTPUT
-        target_cmake_flags="-DLLVM_RELEASE_ENABLE_PGO=OFF"
+
+        # The hendrikmuhs/ccache-action action does not support installing sccache
+        # on arm64 Linux.
+        if [ "$target" = "Linux-ARM64" ]; then
+          echo ccache=ccache >> $GITHUB_OUTPUT
+        else
+          echo ccache=sccache >> $GITHUB_OUTPUT
+        fi
+
+        if [ "${{ runner.os }}" = "Linux" ]; then
----------------
carlocab wrote:

```suggestion
        if [ "$RUNNER_OS" = "Linux" ]; then
```
We don't need workflow interpolation here, and it's better to avoid it if we don't need it: https://docs.github.com/en/actions/security-for-github-actions/security-guides/security-hardening-for-github-actions#using-an-intermediate-environment-variable

In general I'd prefer to remove all workflow interpolation (even in instances where it is safe) to make auditing easier, but that would require plenty of changes across all workflows.

https://github.com/llvm/llvm-project/pull/120786