Implement a missing portion of Ada 2005's AI05-0049-1 for subprogram
Ada.Directories.Name_Case_Equivalence so that user programs can account for
operating system differences in case sensitivity.

------------
-- Source --
------------

--  main.adb

with Ada.Directories; use Ada.Directories;
with Ada.Text_IO;     use Ada.Text_IO;
procedure Main is
begin

  --  Directory layout:
  --     /empty +-- Nothing...
  --
  --     /mutliplefiles +-- "TEST1.TXT"
  --                    |
  --                "test1.txt"
  --
  --     /singlefile +-- "test1.txt"
  --
  --     /noncasable +-- "!"
  --

  Put_Line (Name_Case_Equivalence ("./empty")'Image);
  Put_Line (Name_Case_Equivalence ("./multiplefiles")'Image);
  Put_Line (Name_Case_Equivalence ("./singlefile")'Image);
  Put_Line (Name_Case_Equivalence ("./multiplefiles/test1.txt")'Image);
  Put_Line (Name_Case_Equivalence ("./singlefile/test1.txt")'Image);
  Put_Line (Name_Case_Equivalence ("./noncaseable/!")'Image);
end;

----------------------------
-- Compilation and Output --
----------------------------

& gnatmake -q main.adb
& main
CASE_SENSITIVE
CASE_SENSITIVE
CASE_SENSITIVE
CASE_SENSITIVE
CASE_SENSITIVE
CASE_SENSITIVE

2018-05-30  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* libgnat/a-direct.adb, libgnat/a-direct.ads (Name_Case_Equivalence):
	Add implementation.
	(Start_Search): Modify to use Start_Search_Internal
	(Start_Search_Internal): Add to break out an extra flag for searching
	case insensative due to the potential for directories within the same
	OS to allow different casing schemes.
	* sysdep.c (__gnat_name_case_equivalence): Add as a default fallback
	for when the more precise solution fails.

From-SVN: r260942