When we add an entry to the implicit with chain of a unit while adding
an RTS unit, we must not mark it as a ignored ghost statement because it
points to the next with in the chain.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* rtsfind.adb (Maybe_Add_With): Ensure that the added "with" is
	never marked as ignored ghost code.