There is a llvm-toolset-10 build out on the centos buildlogs. The rpms are unsigned since they never got published out to the official centos scl repos; thus they won't be trusted by default. Also note that since some of the packages in llvm-toolset have a dependency on devtoolset you will need to ensure you have the right devtoolset repo installed as well.

Add repo for devtoolset

sudo yum install centos-release-scl-rh

Create a custom repo pointing to buildlogs

sudo bash -c 'cat << EOF > /etc/yum.repos.d/llvmtoolset-build.repo
[llvmtoolset-build]
name=LLVM Toolset 11.0 - Build
baseurl=https://buildlogs.centos.org/c7-llvm-toolset-11.0.x86_64/
gpgcheck=0
enabled=1
EOF'

Install the llvm toolset packages you need

sudo yum install --nogpgcheck llvm-toolset-11.0-clang-tools-extra llvm-toolset-11.0-clang

Enable the llvm toolset

echo "source /opt/rh/llvm-toolset-11.0/enable" >> ~/.bashrc
source ~/.bashrc