Use a newer clang for sysroot-only build

.github/workflows/main.yml

@@ -164,9 +164,10 @@ jobs:
       - uses: ./.github/actions/checkout
       - uses: ./.github/actions/install-deps
       - run: cargo install wasm-component-ld@0.5.12
+      - run: apt-get update -y && apt-get install -y clang-20
       - run: |
           cmake -G Ninja -B build -S . \
-            -DCMAKE_C_COMPILER=/usr/lib/llvm-18/bin/clang \
+            -DCMAKE_C_COMPILER=/usr/lib/llvm-20/bin/clang \
             -DCMAKE_SYSTEM_NAME=WASI \
             -DWASI_SDK_INCLUDE_TESTS=ON \
             -DWASI_SDK_CPU_CFLAGS="" \