It would be helpful to find out i.e. to ask the person who made the comment.
It has been far too long since I compiled any C - so take with a grain of salt - but I think it is hard to generalize about compiling a large project because it depends on
- the sophistication of the build environment i.e. its ability to detect opportunities for parallelism, to use those opportunities and to adjust (limit) itself to the available CPU resources
- there’s a fair bit of disk I/O going on to muddy the picture for a straight CPU speed comparison (maybe the poster has RAID-0 dual PCIe 3.0x4 NVMe disks, but you don’t
) - and amount of RAM available to cache disk affects things too - the specific dependencies between modules make it hard to generalize across projects i.e. a flatter structure of layers will parallelize better than a deeper structure of layers
I understand that the poster was basically compiling the same thing, which could eliminate the first and third bullet points - but then you get complications about whether the compiler on x86 is performing more substantial optimization (which makes the resulting code better but makes the compile take longer).
That’s why I went for a more vanilla example - a CPU-intensive iterative algorithm
See also Raspberry pi software information - #30 by kieran
(NB: That’s running something that actually would parallelize well but I believe has not been written to do that.) Any followup comments on that topic are probably best in that topic.