The code for this chapter is located in the /chapter-08-tetris folder of the learn-webassembly repository. There are two directories within /chapter-08-tetris: the /output-native folder, which contains the original (pre-ported) code and the /output-wasm folder, which contains the ported code.
If you want to use VS Code's Task feature for the native build step, you'll need to open the /chapter-08-tetris/output-native folder in VS Code, not the top-level /learn-webassembly folder.