Building non resource demanding techs in the main process instead of the forked one

Building non resource demanding techs in the main process instead of the forked one seems to give some speed boost on a real project.

```
bem make                      85.941ms
bem make  -w 2                80.307ms
IN_PROCESS=1 bem make         74.078ms
IN_PROCESS=1 bem make -w 2    73.692ms
```