In-source build with `make install' step results in webkit missing from QT_CONFIG, even if webkit was enabled

 
$ ./configure -nokia-developer -no-pch -silent -nomake demos -nomake examples -prefix $PWD/_install
$ make -j25
$ make -j1 install
$ mkdir -p ~/TEMPORARY/qmaketest
$ cd ~/TEMPORARY/qmaketest
$ echo 'message(QT_CONFIG is $$QT_CONFIG)' > qmaketest.pro
$ ~/build/qt/4.7/_install/bin/qmake
Project MESSAGE: QT_CONFIG is minimal-config small-config medium-config large-config full-config qt3support phonon phonon-backend accessibility opengl reduce_exports ipv6 clock-gettime clock-monotonic mremap getaddrinfo ipv6ifname getifaddrs inotify png system-freetype system-zlib nis iconv glib gstreamer dbus openssl x11sm xshape xvideo xsync xrender mitshm fontconfig xkb alsa xmlpatterns multimedia audio-backend svg script scripttools declarative debug private_tests