For installing eric6 I do the following:

1.Mageia's qt5 (version 5.4.0) installed. Found qmake in /usr/bin .

2.Downloaded:van Riverbank QScintilla 2.9
I follow advice Baz Walter of Riverbank:
=====
If you want to install QScintilla for Qt5, you will have to tweak the source code a little to get things to work properly.

So, starting from some clean sources, open up the Qt4Qt5/features/qscintilla2.prf file in a text editor, and replace each line that looks exactly like this:

    LIBS += -lqscintilla2

with this:

    LIBS += -lqscintilla2_qt5

This is to ensure that you can safely install QScintilla for both Qt4 and Qt5.

For the same reason, open the Qt4Qt5/qscintilla.pro file and replace this line:

    TARGET = qscintilla2

with this:

    TARGET = qscintilla2_qt5

Once that has been done, you need to make sure that the correct features file will be found (this is the most likely cause of your build errors). So before you start re-building anything, do the following:

    $ cd Qt4Qt5
    $ export QMAKEFEATURES="$PWD/features"

You should also remove any QScintilla libs that you installed previously (i.e. the libqscintilla2.so* files that probably ended up in /usr/lib64). These files will currently have the same names as those used by Qscintilla for Qt4, which is why the changes made above are needed.

With that done, re-build QScintilla2, and then have another go at building the Qscintilla Python bindings.
-- 
Regards
Baz Walter
=====

Being in dir /Qt4Qt5 I did $ export QMAKEFEATURES="$PWD/features"
To keep the export do not leave this dir (for qmake and make)
And than qmake qscintilla.pro
Than make
And as root make install
Up to now no problems

3.Installing sip
I downloaded sip 4.16.8 (from Riverbank)
Sometimes for sip python.h is missing so I installed lib64python3-devel
but I do not know whether this is necessary.
I did python3 configure.py
Than make and
as root make install.
No problems.

4.Installing PyQt5.
I downloaded PyQt-gpl-5.4.2 (from Riverbank)
Than python3 configure.py
Than make (takes about 25 minutes)
Than as root make install
No problems.

5.Installing the QScintilla-gpl-2.9 Python bindings:
in the dir /Python: python3 configure.py --pyqt=PyQt5 --qmake=/usr/bin/qmake
Than make
And than as root make install.
No problems.

6.Installing eric6.0.6
As root python3 install.py
The result is:

===
root@localhost eric6-6.0.6]# python3 install.py 
Checking dependencies
Python Version: 3.4.3
Found PyQt5
Found QScintilla2
Found QtGui
Found QtNetwork
Found QtPrintSupport
Found QtSql
Found QtSvg
Sorry, please install QtWebKit.
Error: No module named 'PyQt5.QtWebKit'
Sorry, please install QtWebKitWidgets.
Error: No module named 'PyQt5.QtWebKitWidgets'
Found QtWidgets
[root@localhost eric6-6.0.6]#
===

QUESTION:
I tried a lot of things but cannot find QtWebKit and QtWebKitWidgets.
Please help,

Thanks