cannot disable WARNINGS_ARE_ERRORS for a single module

Hi, I am building for Android (32bit) and there are some warnings, which are errors. If I build the full qt5, I can pass "-no-warnings-are-errors" to configure, which is translated to "-DWARNINGS_ARE_ERRORS=OFF" for cmake and it works. Now I want to build only qtdeclarative. I call CMake with "-DWARNINGS_ARE_ERRORS=OFF" and it tells me

Manually-specified variables were not used by the project:

WARNINGS_ARE_ERRORS

and afterwards the build fails because of the warnings which are errors.
How can I disable the "warnings are errors" for a single module?
Here is my full CMake command:

/usr/bin/cmake -GNinja -DWARNINGS_ARE_ERRORS=OFF -DBUILD_WITH_PCH=OFF -DCMAKE_TOOLCHAIN_FILE=/home/andreasbuhr/Android/Sdk/ndk/21.3.6528147/build/cmake/android.toolchain.cmake -DANDROID_SDK_ROOT=/home/andreasbuhr/Android/Sdk -DANDROID_STL="c++_shared" -DQT_HOST_PATH=$basedir/qtbase -DCMAKE_FIND_ROOT_PATH=$basedir/qtbase-android -DFEATURE_developer_build=ON -DCMAKE_CXX_FLAGS=-Wfatal-errors -DQT_BUILD_EXAMPLES=ON /home/andreasbuhr/development/qtdev/qtdeclarative

The full set of commands is attached.