Basically if you had to get a distro out the door, and 100 days to do it, given your example, if the code was written in C with a C compiler, you'd be done 5% quicker.
It's not the sort of thing you can measure once and just forget about.
Then of course by moving to a C++ compiler, the temptation is to use features that take forever to compile!
Then of course by moving to a C++ compiler, the temptation is to use features that take forever to compile!