Setting c++ standard does not add -std argument to default build task

[ghost]

Bug type: Language Service

Describe the bug

• OS and Version:
  • Local: Microsoft Windows 10 Pro Education 10.0.19041 Build 19041
  • Remote: WSL2 Ubuntu 20.04.3 LTS
• VS Code Version: 1.59.1 system setup
• C/C++ Extension Version: 1.6.0
• Other extensions you installed (and if the issue persists after disabling them):
  • Local (enabled)
  • Remote Development Pack
    • Remote - WSL
  • Remote (enabled)
  • YAML
  • Clang-Format
• If using SSH remote, specify OS of remote machine: NA
• A clear and concise description of what the bug is, including information about the workspace (i.e. is the workspace a single project or multiple projects, size of the project, etc). Single folder workspace (without workspace file). After you change the c++ standard through the ui provided by the c++ extension, if you configure a default build task the "args" property does not include the "-std" argument which lets the compiler know which c++ version to use.

Steps to reproduce

1. Ctrl + Shift + P > C/C++: Edit Configurations (UI)
2. Change C++ standard to c++20
3. Create a main.cpp file in the folder
4. Ctrl + Shift + P > Tasks: Configure Default Build Task > C/C++: g++ build active file (compiler = /usr/bin/g++)
5. Note when tasks.json opens, the -std argument is missing under the args property
6. Add some c++ code that uses a c++20 feature in main.cpp
7. Ctrl + Shift + B
8. Compiler error

Expected behavior

At step 5, there should be a -std argument in the args property of the task that is set to the c++ standard selected by the user. If none is selected through the UI, then it should match the default one that you can set through vscodes settings UI under extensions > C/C++. If that is not set, then it should use intellisense default standard.

Code sample and logs

• Code sample

  
  #include <iostream>
  #include <iterator> // for std::size

int main() { char myString[]{ "string" }; const int length{ static_cast(std::size(myString)) }; // const int length{ sizeof(myString) / sizeof(myString[0]) }; // use instead if not C++17 capable std::cout << myString << " has " << length << " characters.\n";

for (int index{ 0 }; index < length; ++index)
    std::cout << static_cast<int>(myString[index]) << ' ';

std::cout << '\n';

return 0;

}

from https://www.learncpp.com/cpp-tutorial/c-style-strings/
- Configurations in `c_cpp_properties.json`
```json
{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/g++",
            "cStandard": "gnu17",
            "intelliSenseMode": "linux-gcc-x64",
            "cppStandard": "c++20"
        }
    ],
    "version": 4
}

• Logs from running C/C++: Log Diagnostics from the VS Code command palette

  
  -------- Diagnostics - 8/27/2021, 3:44:00 PM
  Version: 1.6.0
  Current Configuration:
  {
  "name": "Linux",
  "includePath": [
      "${workspaceFolder}/**"
  ],
  "defines": [],
  "compilerPath": "/usr/bin/g++",
  "cStandard": "gnu17",
  "intelliSenseMode": "linux-gcc-x64",
  "cppStandard": "c++20",
  "compilerPathIsExplicit": true,
  "cStandardIsExplicit": true,
  "cppStandardIsExplicit": true,
  "intelliSenseModeIsExplicit": true
  }
  Translation Unit Mappings:
  [ /home/user/files/code/[SNIPPED]/main.cpp ]:
  /home/user/files/code/[SNIPPED]/main.cpp
  Translation Unit Configurations:
  [ /home/user/files/code/[SNIPPED]/main.cpp ]:
  Process ID: 2296
  Memory Usage: 12 MB
  Compiler Path: /usr/bin/g++
  Includes:
      /usr/include/c++/9
      /usr/include/x86_64-linux-gnu/c++/9
      /usr/include/c++/9/backward
      /usr/lib/gcc/x86_64-linux-gnu/9/include
      /usr/local/include
      /usr/include/x86_64-linux-gnu
      /usr/include
  Standard Version: c++20
  IntelliSense Mode: linux-gcc-x64
  Other Flags:
      --g++
      --gnu_version=90300
  Total Memory Usage: 12 MB

------- Workspace parsing diagnostics ------- Number of files discovered (not excluded): 2843

- Logs from [the language server logging](https://code.visualstudio.com/docs/cpp/enable-logging-cpp#_enable-logging-for-the-language-server)

**Screenshots**
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[sean-mcmanus]

This is a duplicate of https://github.com/microsoft/vscode-cpptools/issues/7268 .