Custom build - webengine libraries not copied to installation

Hello community,

i am trying to build and use a custom build of Qt for my app.

I`ve checked out the 5.5 branch of Qt and setup the requirements following this guide: https://wiki.qt.io/Building_Qt_5_from_Git

Then I ran the configure-command in the source dir (/opt/qt-src/qt5/) as follows:
./configure -confirm-license -opensource -release -nomake tests -nomake examples

Configure runs normally, no errors at all.

Then I run qmake within the qtwebengine directory to change a Gyp variable before build.

Then I build it using this command:
./make -j4

And after that install:
./make install

Also both run with no errors or aborts. I can also see the build progress of qtwebengine/chromium ([1000/10600]).

Finally I copy over the installation files from "/usr/local/Qt-5.5.1" to my developer machine to the same directory.

After this, I add it as kit/version to QtCreator, no complains at all.

But now ff I try to compile my app with this installation, the compiler gives me the following error:
"QT: unknown module qtwebenginewidgets".

With the Qt 5.5 standard installation it worked before.

If I take a look at the installation dir "/usr/local/Qt-5.5.1/lib/" on the developer machine there are all webengine-related libraries missing (libQtWebEngineCore.so and so on).
In the source dir on the compilation machine ("/opt/qt-src/qt5/qtwebengine/lib") all libraries like libQtWebEngineCore.so and so on are there. So they were definitely built.

But why are`nt they copied to the installation directory to the libs ?

Please help !