When I select Qt modules from the Qt modules window, a semicolon like "core;sql;widgets;" is added at the end of the Qt modules. Any change in the project causes the whole project to compile. When I manually fixed the semicolon at the end ("core;sql;widgets"), the problem disappeared.

If there is a semocolon at the end, each build starts with the following line.

1>Reading Qt configuration (C:/Qt/Qt5.10.0/5.10.0/msvc2017_64/bin/qmake)