Make it explicit and definite that QMake does not accept compiler settings given by Qt Creator

C or C++ compiler that you use to build the project. You can add compilers to the list if they are installed on the development PC, but were not detected automatically. For more information, see Add compilers.
This setting is used to tell the code model which compiler is used. If your project type and build tool support it, Qt Creator also tells the build tool to use this compiler for building the project.