problemMatcher assumes relative paths

[paulkilroy]

In the code below, it assumes all paths from gcc, etc are relative -- but they are not. The fix is describe at the link below, the change is simple and seems to work on mac and linux. Change the word "relative" to "autoDetect"

https://code.visualstudio.com/docs/debugtest/tasks#_output-behavior

Note that the file, line, and message properties are mandatory. The fileLocation specifies whether the file paths that are produced by the task output and matched in the problem are absolute or relative. If the task produces both absolute and relative paths, you can use the autoDetect file location. With autoDetect, paths are first tested as absolute paths, and if the file doesn't exist then the path is assumed to be relative.

"problemMatchers": [
      {
        "name": "platformio",
        "owner": "cpp",
        "fileLocation": [
          "relative",
          "${workspaceFolder}"
        ],
        "pattern": {
          "regexp": "^([^:\\n]+):(\\d+):(\\d+):\\s+(warning|error):\\s+(.*)$",
          "file": 1,
          "line": 2,
          "column": 3,
          "severity": 4,
          "message": 5
        }
      }
    ],