vscode dune build task

tasks.json

{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build all",
            "group": "build",
            "type": "shell",
            "command": "opam exec -- dune build",
            "options": {
                "env": {
                    "OCAML_ERROR_STYLE": "short"
                }
            },
            "problemMatcher": {
                "base": "$ocamlc",
                "source": "dune"
            }
        }
    ]
}