Support custom targets on the Mac

All the custom targets that are defined in a .pro file
EXAMPLES:-------------------------------------------

1. mesages target
   QMAKE_EXTRA_TARGETS = messages
   messages.depends = MessageData.h

QMAKE_EXTRA_TARGETS += Messages.h
Messages.h.depends = Messages.mc
Messages.h.commands = msgc -c Messages.mc

QMAKE_EXTRA_TARGETS += vutils
vutils.commands = time ${MAKE} -C $(VLibDir)/VUtils/src all;\

END EXAMPLES:--------------------------------------

work great on unix systems, but on the Mac are not read into the xcode generated project.