[flohofwoe]

TBF, C doesn't suffer from the "headers cause slow builds" problem of C++, because C headers usually only contain a handful of declarations (e.g. the C stdlib headers are a couple of hundred lines of function prototypes and struct declarations, not tens of thousands of lines of gnarly template code like C++ stdlib headers).

[Gibbon1]

When I've looked at what's going on with gcc what I see is most of the code being compile is header files. It's probably 90% headers and 10% actual code. And then there is all the dependency files it's reading. Though to be fair I think a lot of that is not so much trying to make C compile fast but to make C++ compile fast.