[Ada] Cleanup and efficiency improvements

[Ada] Cleanup and efficiency improvements

gcc/ada/

	* gen_il-gen.adb: Generate getters and setters with much of the
	code inlined. Generate code for storing a few fields in the node
	header, to avoid the extra level of indirection for those
	fields. We generate the header type, so we don't have to
	duplicate hand-written Ada and C code to depend on the number of
	header fields.  Declare constants for slot size. Use short names
	because these are used all over.  Remove
	Put_Low_Level_Accessor_Instantiations, Put_Low_Level_C_Getter,
	which are no longer needed.  Rename
	Put_High_Level_C_Getter-->Put_C_Getter.
	* atree.ads, atree.adb: Take into account the header slots.
	Take into account the single Node_Or_Entity_Field type.  Remove
	"pragma Assertion_Policy (Ignore);", because the routines in
	this package are no longer efficiency critical.
	* atree.h: Remove low-level getters, which are no longer used by
	sinfo.h and einfo.h.
	* einfo-utils.adb: Avoid crash in Known_Alignment.
	* live.adb, sem_eval.adb: Remove code that prevents Node_Id from
	having a predicate.  We don't actually add a predicate to
	Node_Id, but we want to be able to for temporary debugging.
	* sinfo-utils.adb: Remove code that prevents Node_Id from having
	a predicate.  Take into account the single Node_Or_Entity_Field
	type.
	* sinfo-utils.ads: Minor.
	* table.ads (Table_Type): Make the components aliased, because
	low-level setters in Atree need to take 'Access.
	* treepr.adb: Take into account the single Node_Or_Entity_Field
	type.  Make some code more robust, so we can print out
	half-baked nodes.
	* types.ads: Move types here for visibility purposes.
	* gcc-interface/gigi.h, gcc-interface/trans.c: Take into account
	the Node_Header change in the GNAT front end.
	* gcc-interface/cuintp.c, gcc-interface/targtyps.c: Add because
	gigi.h now refers to type Node_Header, which is in sinfo.h.