[chubot]

A lot of the bottleneck is the header structure: the size of the translation units (.c files with headers expanded transitively) is often quadratic with respect to overall codebase size.

If you fix that, then linking can take a long time too. (Not sure on the details, but it's a "global" algorithm to fix up all the pointer offsets)

Incremental builds will be slow if you structure your code in such a way that you often have to touch a header file, and that header file requires recompiling all translation units.

In short, you have to be super careful about structuring your code in C/C++ if you want fast build times, and approximately zero of the industrial codebases I've seen do this. (Well there was one, but it was all written by a single person, which is not surprising.)