Use 18 for RISCV64

.github/workflows/ci.yml

@@ -272,8 +272,8 @@ jobs:
         run: |
           wget https://apt.llvm.org/llvm.sh
           chmod +x llvm.sh
-          sudo ./llvm.sh 20
-          echo "/usr/lib/llvm-20/bin" >> $GITHUB_PATH
+          sudo ./llvm.sh 18
+          echo "/usr/lib/llvm-18/bin" >> $GITHUB_PATH
 
       - name: Build Odin
         run: ./build_odin.sh release