[ci] add llvm ppa

Author: JSUYA

.github/workflows/build.yml

@@ -30,6 +30,8 @@ jobs:
 
       - name: Install dependencies
         run: |
+          wget -O - https://apt.llvm.org/llvm.sh
+          sudo ./llvm.sh 12
           sudo apt-get update
           sudo apt-get install -y clang-12 rpm2cpio cpio binutils-${{ matrix.triple }}