FindQt4: Fix QT_QMAKE{_QMAKE => }_EXECUTABLE typo

The parent commit accidentally referenced QT_QMAKE_QMAKE_EXECUTABLE
which does not exist.  Use QT_QMAKE_EXECUTABLE instead.

Reported-by: m.hergarden@euphoria-it.nl
FindQt4: If Qt5 is in CMAKE_PREFIX_PATH, be sure to find Qt4 includes.
Merge topic 'findqt4-withqt5' into next

bd27c64 FindQt4: If Qt5 is in CMAKE_PREFIX_PATH, be sure to find Qt4 includes.
db00592 FindQt4: Fix QT_QMAKE{_QMAKE => }_EXECUTABLE typo