A tie between the Linux kernel and LLVM (specifically Clang). Also making game engines gets pretty hefty quite quickly. That's just open source work though. I've worked on larger systems at some Big Tech that were unwieldy, too.
And at no point were you bothered by the timewaste C/C++ compiling (and especially, unavoidable linking!) brings to your work process, CI process and general ability to quickly debug and iterate on a hard problem?
It depends on the problem. For some problems where you’re spending time mostly thinking, and relatively little time actually typing code, the compile times don’t really matter that much.
For LLVM for example, with clangd configured to do code completion and syntax checking in the editor, you don’t really have to do as many build/test cycles.
That said, I think fast compile times are important for the other use cases.
