bug#44184: Building icecat does not always respect the number of cores

I can confirm that bug on current Guix system. I also have the feeling that it's not only during rustc parts, I see it while having gcc compiling C++ stuff as well...

bug#44184: Building icecat does not always respect the number of cores

Dear guix, I have configured the guix daemon to use 1 core by default, so that unattended upgrades and CI jobs will not fill my system memory and crush my computer. However, I noticed that in a precise time frame of compiling icecat, the number of cores were not respected and all my cores were co