This patch adds SPARK annotations to subprograms from
System.Address_To_Access_Conversions. To_Pointer is considered to have
no global items, if the returned value has no aliases. To_Address is
forbidden in SPARK because addresses are not handled.

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

gcc/ada/

	* libgnat/s-atacco.ads (To_Pointer): Add Global => null.
	(To_Address): Add SPARK_Mode => Off.