尝试在Rhel 7机器上安装llvm-toolset-7 说明首先要启用rhel-7-server-devtools-rpms。但是，它对我不可用。
subscription-manager repos --enable rhel-7-server-devtools-rpms
Error: 'rhel-7-server-devtools-rpms' does not match a valid repository ID. Use "subscription-manager repos --list" to see valid repositories.