cmake: multi-ABI Android builds do not work in-tree

Setup: Qt 6.4.0 from the installer: all 4 Android platforms + Linux desktop

Building an app for in multi-ABI mode inside the source directory with something like:

qt-cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DQT_HOST_PATH=... -DQT_ANDROID_SDK_BUILD_TOOLS_REVISION=30.0.3 \ -DANDROID_NATIVE_API_LEVEL=23  -DQT_ANDROID_BUILD_ALL_ABIS=TRUE  -DANDROID_NDK_ROOT=${ANDROID_SDK_ROOT}/ndk/... -DANDROID_SDK_ROOT=${ANDROID_SDK_ROOT} .

correctly detects all ABIs:

Configuring '<app>' for the following Android ABIs: arm64-v8a (default), armeabi-v7a, x86, x86_64

but the sub-cmake runs for the extra (non-default) ABIs are then thoroughly confused and think they are for am64-v8a as well:

Found android platform plugin at: .../Qt/6.4.0/android_arm64_v8a/./plugins/platforms/libplugins_platforms_qtforandroid_arm64-v8a.so

And in the end, the build fails with with cmake --build complaining:

Error: could not load cache

You can see a full log of such a failed run in this GitHub CI log for an open-source project of mine: I have attached the relevant part of the build log, but the full one is also available until it expires: https://github.com/rgriebl/brickstore/actions/runs/3290035763/jobs/5422338121

Switching the CI to do a shadow build instead, instantly made the multi-ABI build work.