Add LLVM-13 installation to Docker setup (apache#9498)

* Installs LLVM 13 in for Ubuntu 18.04 Docker images
 * This is needed as a requirement for apache#9425

docker/install/ubuntu1804_install_llvm.sh

@@ -41,10 +41,22 @@ echo deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-12 main\
 echo deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic-12 main\
      >> /etc/apt/sources.list.d/llvm.list
 
+echo deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-13 main\
+     >> /etc/apt/sources.list.d/llvm.list
+echo deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic-13 main\
+     >> /etc/apt/sources.list.d/llvm.list
+
 echo deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic main\
      >> /etc/apt/sources.list.d/llvm.list
 echo deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic main\
      >> /etc/apt/sources.list.d/llvm.list
 
 wget -q -O - http://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
-apt-get update && apt-get install -y llvm-9 llvm-10 llvm-11 llvm-12 clang-9 libclang-9-dev clang-10 libclang-10-dev clang-11 libclang-11-dev clang-12 libclang-12-dev
+
+apt-get update && apt-get install -y \
+     llvm-9 llvm-10 llvm-11 llvm-12 llvm-13 \
+     clang-9 libclang-9-dev \
+     clang-10 libclang-10-dev \
+     clang-11 libclang-11-dev \
+     clang-12 libclang-12-dev \
+     clang-13 libclang-13-dev