Build script fails to update primitives folder

[rachitnigam]

When running the cargo build, the following warning is displayed:

% cargo build                                  
warning: calyx@0.6.1: Failed to create the `primitives` folder. Importing `primitives` will require passing an explicit `-l` when running the Calyx compiler. Error: Directory not empty (os error 66)

This is coming from the build.rs file responsible for replacing the globally linked primitives/ folder. The script itself is quite janky. I think we should switch to using fragment or something and make it more robust.