Qt4: Use generator expression in COMPILE_DEFINITIONS

Commit 5bb53f6b (cmTarget: Deprecate COMPILE_DEFINITIONS_ properties
with a policy., 2013-12-30) deprecated the config-specific
COMPILE_DEFINITIONS_* properties in favour of using generator
expressions.

Set the directory property in UseQt4.cmake to match the
INTERFACE_COMPILE_DEFINITIONS on the Qt4::QtCore and Qt5::Core
IMPORTED targets.  Setting QT_NO_DEBUG is sufficient because qglobal.h
sets the corresponding QT_DEBUG definition if required.
Merge topic 'update-Qt4-COMPILE_DEFINITIONS' into next

131a31dc Qt4: Use generator expression in COMPILE_DEFINITIONS