It would be useful to have an option to "sim build" to disable parallel build. We could then ask users to run with this when they have build problems so that we can clearly see the error.
This would need a more structured "make" simfactory variable. Perhaps there could be a MAKE_TASKS variable, and then we could set "make = make -j@MAKE_TASKS@". MAKE_TASKS could be set either by an entry in the machine database, an option in the optionlist, or by simfactory when a --no-parallel-build option was set.