[Ada] AI12-0260 Functions Is_Basic and To_Basic in Wide_Characters.Handling

[Ada] AI12-0260 Functions Is_Basic and To_Basic in Wide_Characters.Handling

2020-06-15  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* libgnat/a-wichha.ads, libgnat/a-wichha.adb,
	libgnat/a-wichun.ads, libgnat/a-wichun.adb (Is_Basic, To_Basic):
	New.
	* libgnat/s-utf_32.ads, libgnat/s-utf_32.adb (Is_UTF_32_Basic,
	To_UTF_32_Basic, Decomposition_Search): New subprograms.
	(Unicode_Decomposition): New table.