2019-12-16  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* impunit.adb: Add a-nbnbin, a-nbnbre, a-nubinu to Ada 2020
	units.
	* Makefile.rtl: Enable new file.
	* libgnat/a-nbnbin.adb, libgnat/a-nbnbin.ads,
	libgnat/a-nbnbre.adb, libgnat/a-nbnbre.ads,
	libgnat/a-nubinu.ads: New files. Provide default standalone
	implementation of Ada.Numerics.Big_Numbers.Big_* based on
	System.Generic_Bignum.
	* libgnat/a-nbnbin__gmp.adb: Alternate implementation of
	Ada.Numerics.Big_Numbers.Big_Integers based on GMP. Not enabled
	for now.
	* libgnat/s-bignum.ads, libgnat/s-bignum.adb: Now a simple
	wrapper on top of s-genbig.ads.
	* libgnat/s-genbig.ads, libgnat/s-genbig.adb: New files, making
	s-bignum generic for reuse in Ada.Numerics.Big_Numbers.

From-SVN: r279418