Added cmake_policy setting for cmake-3.x to avoid warning with Qt usage.

git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/branches/OpenSceneGraph-3.2@14972 16af8721-9629-0410-8352-f15c8da7e697

CMakeLists.txt

@@ -618,6 +618,13 @@ IF(OSG_USE_QT AND NOT ANDROID)
     #If we have found Qt5, let's try to top off by getting the webkit as well
     IF ( Qt5Widgets_FOUND )
         FIND_PACKAGE(Qt5WebKitWidgets QUIET)
+
+        IF(COMMAND cmake_policy)
+            IF(${CMAKE_MAJOR_VERSION} GREATER 2)
+                # Qt5 qt5_use_modules usage was causing "Policy CMP0043 is not set: Ignore COMPILE_DEFINITIONS_<Config> properties." warnings
+                cmake_policy(SET CMP0043 NEW)
+            ENDIF()
+        ENDIF()
     ENDIF()
 
 ENDIF()