[Development] Qt Compilation Speed

[Philippe]

> The change to C++17 makes a huge difference too, regardless of PCH. That 
> #include <algorithm> in qglobal.h adds up to 300 ms in each build without PCH, 
> and a considerable amount with it too. And it gets worse with C++20 and ranges.

I did not notice any sensitive change when switching to C++20 (but not
using ranges).

I am using PCH, which has always been a big winner, at least with MSVC.

Philippe