WebKit build failure - FrameLoader.cpp - member access into incomplete type 'WebCore::Archive'

Build log attached (with just the described problem included, by re-running make after the failure occurred).

Environment includes the relevant:
SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk
MACOSX_DEPLOYMENT_TARGET=10.7
CXXFLAGS=-stdlib=libc++

Configure line was:
../qt-everywhere-opensource-src-5.4.0-beta/configure -sdk macosx10.10 -warnings-are-errors -system-proxies -no-linuxfb -no-directfb -no-dbus -pch -optimized-qmake -v -no-compile-examples -nomake examples -no-glib -opensource -confirm-license -force-debug-info -debug-and-release -prefix `(cd ../qt-everywhere-opensource-src-5.4.0-beta-deploy/; pwd -P)` -icu -no-xcb -I /opt/local/include -L /opt/local/lib

As can be seen in the log, the problem is with dereferencing incomplete types deep inside WebKit.