qmlcachegen not getting invoked on qmake for yocto builds

This issue was primarily reported by GEHC, where-in they recently migrated from Qt 5.15 to Qt 6.5.7 and are using qmake based system in Qt 6.5.7.

As part of performance optimization, they were trying to use qmlcachegen to speed up the execution and the qmlcachegen dosen't seem to get invoked during building their application. 

Tested in below environment and below are the steps to reproduce

1. Download Boot2Qt 6.5.7 for Toradex Applais iMX6
2. Open the project (DropDownWidgetTest) from the attachment using *.pro file
3. Edit the *.pro file and add/enable CONFIG += qtquickcompiler
4. Build the project and we can see in the makefile that the qmlcachegen is not getting invoked and they are not converted to cpp
5. Open the same application (DropDownWidgetTest) using Desktop Qt 6.8.1 MinGW 64-bit
6. Edit the *.pro file and add/enable CONFIG +=qtquickcompiler
7. Build the project and we can see in the makefile that the qmlcahcegen is getting invoked and the qml files are converted to cpp.

Attachment has both the makefiles for Boot2Qt Toradex Appalis iMX6 and Desktop Qt 6.8.1 MinGW 64-bit