Use COMBINE_FILE_LISTS in cmakelists.txt

[MikeHopcroft]

This strategy is used in BitFunnel. Just need to define COMBINE_FILE_LISTS() macro in the top level CMakeLists.txt and then use in the lower level CMakeLists.txt files to replace

if (NATIVEJIT_PLATFORM_WINDOWS)
set(CPPFILES ${CPPFILES} ${WINDOWS_CPPFILES})
set(PUBLIC_HFILES ${PUBLIC_HFILES} ${WINDOWS_PUBLIC_HFILES})
set(PRIVATE_HFILES ${PRIVATE_HFILES} ${WINDOWS_PRIVATE_HFILES})
else (NATIVEJIT_PLATFORM_WINDOWS)
set(CPPFILES ${CPPFILES} ${POSIX_CPPFILES})
set(PUBLIC_HFILES ${PUBLIC_HFILES} ${POSIX_PUBLIC_HFILES})
set(PRIVATE_HFILES ${PRIVATE_HFILES} ${POSIX_PRIVATE_HFILES})
endif (NATIVEJIT_PLATFORM_WINDOWS)