[PyQt] Makespec issue when building PyQt4 against Qt5

[Baz Walter]

Hello

When building PyQt4 against Qt5, I got this error:

     Determining the layout of your Qt installation...
     Error: Unable to find the qmake configuration file
     /usr/share/qt/mkspecs/linux-g++-64/qmake.conf.
     Use the QMAKESPEC environment
     variable to specify the correct platform.

I thought this might be a distro related problem, as the makepsec 
directory was not where it was expected it to be. However, after a bit 
of research, I discovered that the default install directories have been 
changed for Qt5 and a new option "-archdatadir" has been added (details 
can be found here: https://codereview.qt-project.org/#change,35495).

I used QMAKESPEC to solve the immediate problem, but it would be nice if 
the configure script had support for "-archdatadir", as it appears that 
that is what distros should now use to specify the makespec directory 
(as opposed to "-datadir").

--
Regards
Baz Walter