Multi-abi build does not rebuild other targets when there is a change

Steps:

1. Create a minimal Quick project. A rectangle with color 'red' than fills the screen
2. Configure with QT_ANDROID_BUILD_ALL_ABIS=ON . This needs a Qt installation that has at least two Android ABI kits 

~/Qt/<qt_version>/android_<abi>/bin/qt-cmake \
    -DANDROID_SDK_ROOT=~/Android/Sdk \
    -DANDROID_NDK_ROOT=~/Android/Sdk/ndk/26.1.10909125 \
    -DQT_ANDROID_BUILD_ALL_ABIS:BOOL=ON \
    -DQT_USE_TARGET_ANDROID_BUILD_DIR:BOOL=ON \
    -S <source_dir> -B <build_dir> \
    -GNinja 

1. Run ninja in <build-dir>
2. Record the timestamp of the target .so file of the default abi from the root of the build directory.
3. Record the timestamp of the .so files of the target project for other ABIs from builddir/android_abi_builds/*
4. Modify the sources of the project. eg. change the color of the QML Rectangle
5. Run ninja again from the build folder
6. Record the timestamp of the target .so file of the default abi
7. Record the timestamp of the .so files of the target project for other ABIs

Expected results:

• The main .so file should have a newer timestamp
• .so files of the target project for other ABIs also should have a newer timestamp

Actual results:

• The main .so file has a newer timestamp
• The .so files of other ABIs remains the same as the first build

Workaround:

Rebuild the project.