LTO causing QObject::connect to not find signals

While trying to fix the apitrace port to Qt6, I am encountering an issue with signal connections.

QObject::connect is reporting that the signal cannot be found, for any connections made in the executable:

qt.core.qobject.connect: QObject::connect: signal not found in QTimer

I boiled down the issue to an interaction between a library which seems to have nothing in common with Qt - a small image library, which I removed almost all code from, and Qt.
However, it only occurs if the following is set:

set (CMAKE_INTERPROCEDURAL_OPTIMIZATION True)

This enables link time optimization in the compiler if it is supported.
If I remove this, signals work properly. 

Attached is a minimal example reproducing the issue.
I have tested it on Rocky Linux 8, with GCC 11.2.1.