Add caching for downloading compiler-rt

.github/workflows/main.yml

@@ -4,6 +4,8 @@ on: [push, pull_request]
 env:
   RUSTDOCFLAGS: -Dwarnings
   RUSTFLAGS: -Dwarnings
+  RUST_LLVM_VERSION: 18.0-2024-02-13
+  RUST_COMPILER_RT_ROOT: ./compiler-rt
 
 jobs:
   test:
@@ -115,12 +117,18 @@ jobs:
         path: /tmp/.buildx-cache
         key: ${{ matrix.target }}-buildx-${{ github.sha }}
         restore-keys: ${{ matrix.target }}-buildx-
-
+
+    - name: Cache compiler-rt
+      id: cache-compiler-rt
+      uses: actions/cache@v4
+      with:
+        path: compiler-rt
+        key: ${{ runner.os }}-compiler-rt-${{ env.RUST_LLVM_VERSION }}
     - name: Download compiler-rt reference sources
+      if: steps.cache-compiler-rt.outputs.cache-hit != 'true'
       run: |
-        curl -L -o code.tar.gz https://github.com/rust-lang/llvm-project/archive/rustc/18.0-2024-02-13.tar.gz
-        tar xzf code.tar.gz --strip-components 1 llvm-project-rustc-18.0-2024-02-13/compiler-rt
-        echo RUST_COMPILER_RT_ROOT=./compiler-rt >> $GITHUB_ENV
+        curl -L -o code.tar.gz "https://github.com/rust-lang/llvm-project/archive/rustc/${RUST_LLVM_VERSION}.tar.gz"
+        tar xzf code.tar.gz --strip-components 1 llvm-project-rustc-${RUST_LLVM_VERSION}/compiler-rt
       shell: bash
 
     # Non-linux tests just use our raw script