This patch implements unit GNAT.Sets which currently offers a general purpose
membership set. The patch also streamlines GNAT.Dynamic_HTables and GNAT.Lists
to use parts of the same API, types, and exceptions as those used by GNAT.Sets.

2018-09-26  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* gcc-interface/Make-lang.in: Add unit GNAT.Sets to the list of
	front end sources.
	* impunit.adb: Add unit GNAT.Sets to the list of predefined
	units.
	* Makefile.rtl: Add unit GNAT.Sets to the list of non-tasking
	units.
	* libgnat/g-sets.adb: New unit.
	* libgnat/g-sets.ads: New unit.
	* libgnat/g-dynhta.adb (Minimum_Size): Decrease to 8 in order to
	allow for small sets.  Update all occurrences of Table_Locked to
	Iterated.
	(Ensure_Unlocked): Query the number of iterators.
	(Find_Node): Use the supplied equality.
	(Is_Empty): New routine.
	(Lock): Update the number of iterators.
	(Prepend_Or_Replace): Use the supplied equality.
	(Size): Update the return type.
	(Unlock): Update the number of iterators.
	* libgnat/g-dynhta.ads: Update all occurrences of Table_Locked
	to Iterated.  Rename formal subprogram Equivalent_Keys to "=".
	(Bucket_Range_Type, Pair_Count_Type): Remove types.
	(Not_Created, Table_Locked, Iterator_Exhausted): Remove
	exceptions.
	(Hash_Table): Update to store the number of iterators rather
	than locks.
	(Is_Empty): New routine.
	(Size): Update the return type.
	* libgnat/g-lists.adb: Update all occurrences of List_Locked to
	Iterated.
	(Ensure_Unlocked): Query the number of iterators.
	(Length): Remove.
	(Lock): Update the number of iterators.
	(Size): New routine.
	(Unlock): Update the number of iterators.
	* libgnat/g-lists.ads: Update all occurrences of List_Locked to
	Iterated.
	(Element_Count_Type): Remove type.
	(Not_Created, Table_Locked, Iterator_Exhausted): Remove
	exceptions.
	(Linked_List): Update type to store the number of iterators
	rather than locks.
	(Length): Remove.
	(Size): New routine.
	* libgnat/gnat.ads (Bucket_Range_Type): New type.
	(Iterated, Iterator_Exhausted, and Not_Created): New exceptions.

gcc/testsuite/

	* gnat.dg/sets1.adb: New testcase.
	* gnat.dg/dynhash.adb, gnat.dg/linkedlist.adb: Update testcases
	to new API.

From-SVN: r264620