Comment 1 for bug 1548686

I have tested it would _not_ be because of the gccgo-6 (libgcc1), gcc5 or glibc uploads that happened during that timeframe, but also I'm now out of ideas what could be the cause.

In other words, I built older versions of the mentioned packages and checked from build logs they are in use during a build, but it still failed similarly at https://launchpad.net/~timo-jyrinki/+archive/ubuntu/quantal-compiz-unity-testing/+build/9053257/+files/buildlog_ubuntu-xenial-amd64.qtbase-opensource-src_5.5.1+dfsg-14ubuntu2~xenial1~test3_BUILDING.txt.gz