I just disabled LTO for qemu.
It caused what are best described as "weird" assert failures in the test suite.
For comparison here's a good build (without LTO): https://koji.fedoraproject.org/koji/taskinfo?taskID=48188577
And here's a bad build (with LTO): https://koji.fedoraproject.org/koji/taskinfo?taskID=48182910
At some point we'll need to look at what's going on, but right now disabling LTO was the easiest way to work around what might be toolchain bugs.
Rich.