Update COMPILE_DEFINITIONS_X in Qt5CoreMacros.cmake for CMake 3

Qt5CoreMacros produces policy warnings under CMake 3 (RC6) as it sets target properties for COMPILE_DEFINITIONS_RELEASE, COMPILE_DEFINITIONS_DEBUG etc.

"The COMPILE_DEFINITIONS_<CONFIG> directory properties and the COMPILE_DEFINITIONS_<CONFIG> target properties have been deprecated. Instead set the corresponding COMPILE_DEFINITIONS directory property or COMPILE_DEFINITIONS target property and use generator expressions like $<CONFIG:...> to specify per-configuration definitions. See policy CMP0043."

http://www.cmake.org/cmake/help/v3.0/policy/CMP0043.html#policy:CMP0043