I noticed that I was seeing the Go compiler build things in parallel even when I'd set `-j1 --cores 1`. It appears that the compiler, by default, uses the number of CPUs that are available to perform a build, while nixpkgs parallelizes at the directory level.
In order to change the fewest assumptions, this explicitly tells the Go compiler to run single-threaded. The flag's documentation is:
```
-p n
the number of programs, such as build commands or
test binaries, that can be run in parallel.
The default is the number of CPUs available.
```
So this should function as expected. Feedback appreciated!
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