Configure test for SetPlaceHolderText

[Rik]

2/9/17

I answered my own question and changing

#include <Qt/qglobal.h>

to

#include <qglobal.h>

works for both Qt4 and Qt5.  I pushed the change to stable 
(http://hg.savannah.gnu.org/hgweb/octave/rev/039dfdc2d2ad).

--Rik