Recursively get the platform targeted by this module or imported modules

Property definitions

nitc :: platform $ MModule :: target_platform
	# Recursively get the platform targeted by this module or imported modules
	fun target_platform: nullable Platform
	do
		var ltp = local_target_platform
		if ltp != null then return ltp

		for mmodule in in_importation.greaters do
			ltp = mmodule.local_target_platform
			if ltp != null then return ltp
		end

		return null
	end
src/platform/platform.nit:90,2--102,4