setup-cpp/dist/actions/llvm_matcher.json

{
  "problemMatcher": [
    {
      "owner": "llvm",
      "pattern": [
        {
          "regexp": "^(.*?):(\\d+):(\\d*):?\\s+(?:fatal\\s+)?(warning|error):\\s+(.*)$",
          "file": 1,
          "line": 2,
          "column": 3,
          "severity": 4,
          "message": 5
        }
      ]
    }
  ]
}