There seem to be some problems with the new build system in Xcode 10. How do I switch to the old (legacy) build system?
NOTE: While one can apparently still use it for a bit longer (in June 2022), the legacy build system is marked deprecated in Xcode 13.4.1)
You can switch back to the previous (legacy) build system from the menu by
File > Workspace Settings...
(or Project Settings...
):
This brings up a dialog where you can change the Build System
to Legacy Build System
: