Incorrect CMAKE_OSX_ARCHITECTURES passed for ios simulator projects built against Qt 6.8.1

While investigating QTBUG-132830

I noticed this change https://codereview.qt-project.org/c/qt-creator/qt-creator/+/576694

We stopped passing -DCMAKE_OSX_ARCHITECTURES when targeting the iOS simulator sdk.

This results in cmake not passing an explicit -arch on the command line, and the xcode compiler and linker default to using arm64 on an arm mac.

Because Qt 6.8.1 does not ship an arm Qt slice targeting the iphonesimulator SDK, this causes build failures.

Qt does ship an arm64 slice for iphoneos sdk, but that is not usable when targeting the simulator.

I believe Qt Creator should continue to pass a value to CMAKE_OSX_ARCHITECTURES when targeting an ios simulator sdk, so that older versions of Qt continue to work with newer Qt Creators.

In parallel, we need to investigate to handle this without Qt Creator's help for new Qt verisons.