qt5-core not building

[Andrew Hamilton-Wright]

Dear KDE maintainer,

I am attempting to build the devel/qt5-core port (on FreeBSD 11.2) and I am encountering an issue where QT_OPEN_EXCL is undefined:

c++ -c -O2 -pipe -fstack-protector -fno-strict-aliasing -ffunction-sections -fPIC -std=c++1z -fvisibility=hidden -fvisibility-inlines-hidden -fno-exceptions -Wall -W -pthread -DQT_GLIB -DQT_VERSION_STR='"5.9.4"' -DQT_VERSION_MAJOR=5 -DQT_VERSION_MINOR=9 -DQT_VERSION_PATCH=4 -DQT_BOOTSTRAPPED -DQT_NO_CAST_TO_ASCII -DQT_NO_FOREACH -DQT_NO_CAST_FROM_ASCII -DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT -DQT_BUILD_BOOTSTRAP_LIB -DQT_BUILDING_QT -DQT_ASCII_CAST_WARNINGS -DQT_MOC_COMPAT -DQT_USE_QSTRINGBUILDER -DQT_DEPRECATED_WARNINGS -DQT_DISABLE_DEPRECATED_BEFORE=0x050000 -DQT_NO_EXCEPTIONS -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -DQT_NO_DEBUG -I. -I../../../include -I../../../include/QtCore -I../../../include/QtCore/5.11.2 -I../../../include/QtCore/5.11.2/QtCore -I../../../include/QtXml -I../../../include/QtXml/5.11.2 -I../../../include/QtXml/5.11.2/QtXml -I/usr/local/include -I/usr/local/lib/qt5/mkspecs/freebsd-clang -o .obj/qcoreapplication.o ../../corelib/kernel/qcoreapplication.cpp
--- .obj/qtemporaryfile.o ---
../../corelib/io/qtemporaryfile.cpp:254:33: error: use of undeclared identifier 'QT_OPEN_EXCL'
                QT_OPEN_CREAT | QT_OPEN_EXCL | QT_OPEN_RDWR | QT_OPEN_LARGEFILE,
                                ^
1 error generated.
*** [.obj/qtemporaryfile.o] Error code 1

This is a GENERIC kernel.  Uname reports:
	FreeBSD qemg.org 11.2-RELEASE-p4 FreeBSD 11.2-RELEASE-p4 #0: Thu Sep 27 08:16:24 UTC 2018     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64


I don't see anything in the usual places even mentioning this problem.  Do you have any insight into what might have given rise to this?

Thanks,
Andrew.