We shouldn't need incremental builds to be fast. Incremental builds have their own problems, which I'd rather avoid if at all possible. (They're more complex and leave more room for error than rebuilding everything every time.)
I want to compile 100K lines of code or more in less than one second. Compared to that, C++ is slow as molasses.
Maybe UNIX compilers need to do some improvements here.
And when using the experimental modules support it is even faster.