[CI] Add apt repository for clang-11 and llvm-11 (#6256)

- Add specific apt repositories to install clang-11 and llvm-11
 - Fix #6255

diff --git a/docker/install/ubuntu1804_install_llvm.sh b/docker/install/ubuntu1804_install_llvm.sh
index 4f7c9df..292fdde 100755 (executable)
--- a/docker/install/ubuntu1804_install_llvm.sh
+++ b/docker/install/ubuntu1804_install_llvm.sh
@@ -31,6 +31,11 @@ echo deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main\
 echo deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main\
      >> /etc/apt/sources.list.d/llvm.list
 
+echo deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-11 main\
+     >> /etc/apt/sources.list.d/llvm.list
+echo deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic-11 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\