The build system does not work correctly with -DFEATURE_developer_build:BOOL=TRUE

The build system does not define QT_BUILD_INTERNAL after running CMake with -DFEATURE_developer_build:BOOL=TRUE, passing "ON" works, but it may be hard with tools that automatically generate CMake command line (like VS Code CMake plugin). The build system should handle any syntax for CMake booleans (https://cmake.org/cmake/help/latest/command/if.html) in these cases.