compilation error in qtopcua in '5.12'

This is real issue; integration has failed now several times (7) in a row:

Continuous Integration: Failed

Running qmake failed. The CI rejected the staged commits due to the beforementioned reason. Possible reason could be a bug in one of the commits or some more recent change. Please investigate it.

The error was in "qt/qtopcua", revision: a7866244ededbef194dedde9cc3441516847e372

Build log: https://testresults.qt.io/logs/qt/qtopcua/2132e65b8bafc0d35bdedeb8b0a4af10e057acee/LinuxUbuntu_16_04x86_64LinuxUbuntu_16_04x86_64GCCqtci-linux-Ubuntu-16.04-x86_64-2-71bc53DeveloperBuild_OutOfSourceBuild_QtLibInfix_QtNamespace_BuildExamples/12c57ef17e7a04e167a77f039dee3ef942127420/build_1537281152/log.txt.gz

Details: http://ci-files01-hki.intra.qt.io:8080/coin/integration/qt/tqtc-qt5/tasks/1537275408

Tested changes (refs/builds/qtci/tqtc/5.12/1536894717):
https://codereview.qt-project.org/#/q/693bcb02c2f44aed509ef4d831d8bd34e839e7e3,n,z Merge remote-tracking branch 'origin/5.12' into tqtc/5.12
https://codereview.qt-project.org/#/q/3e6bf82aef20a8b2a9ebfcb572dc614f25d8540b,n,z Update submodules on 'tqtc/5.12' in qt5