PrecompileTools causes runtime performance lost

- https://github.com/jinyus/related_post_gen/pull/376

on top of this PR, if I include back a precompile workload:
```julia
@compile_workload begin
print("Precompiling main workload: ")
main()
end
```

I can see that the time recorded at run time becomes worse:
```
Processing time (w/o IO): 19 milliseconds
Processing time (w/o IO): 20 milliseconds
Processing time (w/o IO): 19 milliseconds
```

to

```
Processing time (w/o IO): 25 milliseconds
Processing time (w/o IO): 26 milliseconds
Processing time (w/o IO): 25 milliseconds
```

what's the mechanism for this?