[LyX/master] Update autotools for building with Qt5.

[Enrico Forestieri]

commit 4bdeae27334536164cb7e37da9a9e491075fd682
Date: Sat Jul 19 03:34:28 2014 +0200
Update autotools for building with Qt5.
The option --enable-qt5 allows configuring for Qt5. The default is Qt4.
Nothing special is done with respect to Qt4, apart from pulling in the
correct libraries. Indeed, other than the core and gui libraries, now
also the concurrent and widgets libraries are needed.

Is this --enable-qt5 needed? The version number is already
available, isn't it?

Actually not. QT_DO_PKG_CONFIG asks for the version using
pkg-config --modversion <qtcore>
and <qtcore> is QtCore for Qt4 but Qt5Core for Qt5.
Of course, it can be changed, but I thought that until Qt5 is not
fully supported the extra option makes sense.

[Jean-Marc Lasgouttes]

Post by Enrico Forestieri
Actually not. QT_DO_PKG_CONFIG asks for the version using
pkg-config --modversion <qtcore>
and <qtcore> is QtCore for Qt4 but Qt5Core for Qt5.
Of course, it can be changed, but I thought that until Qt5 is not
fully supported the extra option makes sense.

I see. Thanks.

JMarc