[SOLVED] building a metalbare cross compiler from scratch (custom configured)

[janoc]

I do not have any RPI/BananaPI/whatever on hand, and no time to buy/reallocate one of them in the lab
while the customer wants a copy of the whole building system (which should run on PC), so it's not the point

OK. Well, you could always deliver the build system on an SD card and with its own computer

about what I could to to improve my results: I simply assigned less than 256Mbyte of ram to QEmu (my mistake)
and due to the fact that gcc-build-up eats a lot of ram (more than 512Mbyte if you enable "pipe" instead of "temp files")
the kernel was swapping on /dev/sda1, which was a bottleneck, and assigning 1Gbyte of ram to QEmu improved results

Yeah, 256MB, that's no good - gcc is a huge amount of code, even on a PC with 4GB of RAM the machine will struggle. RAM is by far the most important thing there.