Support debug using vscode for xv6-riscv

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "gdb",
            "request": "attach",
            "name": "Attach to gdbserver",
            "gdbpath": "/opt/riscv/bin/riscv64-unknown-elf-gdb",
            "executable": "kernel/kernel",
            "target": "localhost:26000",
            "remote": true,
            "printCalls": true,
            "cwd": "${workspaceRoot}",
            "valuesFormatting": "parseText"
        }
    ]
}

{
    "tasks": [
        {
            "label": "Build",
            "type": "shell",
            "command": "make",
            "args": [],
            "group": "build",
            "problemMatcher": [
                "$gcc"
            ]
        },
        {
            "type": "cppbuild",
            "label": "C/C++: gcc build active file",
            "command": "/usr/bin/gcc",
            "args": [
                "-fdiagnostics-color=always",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Task generated by Debugger."
        }
    ],
    "version": "2.0.0"
}