Here it is: /usr/lib/qt5/bin/moc -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_XML_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB --include .moc/moc_predefs.h -I/usr/lib/aarch64-linux-gnu/qt5/mkspecs/linux-g++ -I/<<PKGBUILDDIR>>/src -I/<<PKGBUILDDIR>>/src -I/usr/include/tagcoll-2.0.14 -I/usr/include/aarch64-linux-gnu/qt5 -I/usr/include/aarch64-linux-gnu/qt5/QtWidgets -I/usr/include/aarch64-linux-gnu/qt5/QtGui -I/usr/include/aarch64-linux-gnu/qt5/QtXml -I/usr/include/aarch64-linux-gnu/qt5/QtNetwork -I/usr/include/aarch64-linux-gnu/qt5/QtCore -I/usr/include/c++/7 -I/usr/include/x86_64-linux-gnu/c++/7 -I/usr/include/c++/7/backward -I/usr/lib/gcc/x86_64-linux-gnu/7/include -I/usr/local/include -I/usr/lib/gcc/x86_64-linux-gnu/7/include-fixed -I/usr/include/x86_64-linux-gnu -I/usr/include packagesearchimpl.h -o .moc/moc_packagesearchimpl.cpp usr/include/c++/7/bits/stl_relops.:67: Parse error at "std"
Try setting QT_SELECT in debian/rules, that will free you from setting -qt5 on every involved tool.