Fix status badge and LLVM fetching for qemu builds (#362)

The status badge should report the most recent status for the master
branch, not the most recent actions run.

llvm.sh wasn't updated when trunk moved to 14 so was failing to fetch clang-13 (which is now in the llvm-toolchain-focal-13 repo, not the llvm-toolchain-focal repo).  Duplicate the correct logic here rather than relying on the external script.

.github/workflows/main.yml

@@ -106,10 +106,10 @@ jobs:
       # Install the dependencies and clang 13.  Earlier versions of clang don't
       # find the multilib things for this week's Ubuntu filesystem layout.
       run: |
-        wget https://apt.llvm.org/llvm.sh
-        chmod +x llvm.sh
-        sudo ./llvm.sh 13
-        sudo apt install libstdc++-9-dev-${{ matrix.arch }}-cross qemu-user ninja-build lld-13 clang-13
+        wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+        sudo add-apt-repository "deb http://apt.llvm.org/focal/     llvm-toolchain-focal-13  main"
+        sudo apt update
+        sudo apt install libstdc++-9-dev-${{ matrix.arch }}-cross qemu-user ninja-build clang-13 lld-13
     - name: Configure
       run: >
         RTLD_NAME=${{ matrix.rtld }}