Work around Qt6 crash involving LTO

[keithel]

If link time optimization is enabled in a Qt 6 build of qapitrace, signals are not properly connected, and a crash occurs.

Somehow an interaction between the image library and Qt, along with the INTERPROCEDURAL_OPTIMIZATION CMake setting causes this behavior.

Simply disabling link time optimization by setting the INTERPROCEDURAL_OPTIMIZATION qapitrace target property to false fixes the issue.

[okias]

I would wait a bit with merging something like this, since other possible solutions are proposed in https://bugreports.qt.io/browse/QTBUG-115731 .

In worst case it would be nice if it would be guarded by Qt 6 checks.

[keithel]

Actually -- I get this even with Qt5 builds with the compiler, linker and glibc I use. But yeah, I can see waiting until we know more about the underlying issue. It's likely this will just be closed on the Qt side as a compiler issue.

[keithel]

@okias could you verify that my proposed fix works for you (avoids the crash, and allows signals to be connected properly, and the UI to be functional) ?

I want to make sure it isn't just a weird environment issue in my case - given that the Qt R&D folks are saying that it is due to a design flaw in the ABI of x86_64, corrected by gcc 12+binutils 2.36..

[okias]

I would prefer the workaround to be applied only where necessary, such as detecting or defining broken configurations. If it's not easily possible, then I suppose I would be okay with it as it is.

[keithel]

It sounds like this may be fixed in Qt by some changes in the cmake rules, as it appears that adding -fPIC to the linker line fixes the problem - according to Alexandru Croitor. I think we just let this PR sit until QTBUG-115731 is fixed or otherwise closed. I'll make narrower changes when it is more clear as to what to do.