[Ada] Annotate libraries with returning annotation

[Ada] Annotate libraries with returning annotation

This patch annotates SPARK-annotated libraries with returning
annotations (Always_Return, Might_Not_Return) to remove the warnings
raised by GNATprove about missing annotations.

gcc/ada/

	* libgnarl/a-reatim.ads, libgnat/a-cfdlli.ads,
	libgnat/a-cfhama.ads, libgnat/a-cfhase.ads,
	libgnat/a-cfinse.ads, libgnat/a-cfinve.ads,
	libgnat/a-cforma.ads, libgnat/a-cforse.ads,
	libgnat/a-chahan.ads, libgnat/a-cofove.ads,
	libgnat/a-cofuma.ads, libgnat/a-cofuse.ads,
	libgnat/a-cofuve.ads, libgnat/a-nbnbin.ads,
	libgnat/a-nbnbre.ads, libgnat/a-ngelfu.ads,
	libgnat/a-nlelfu.ads, libgnat/a-nllefu.ads,
	libgnat/a-nselfu.ads, libgnat/a-nuelfu.ads,
	libgnat/a-strbou.ads, libgnat/a-strfix.ads,
	libgnat/a-strmap.ads, libgnat/a-strunb.ads,
	libgnat/a-strunb__shared.ads,  libgnat/a-strsea.ads,
	libgnat/a-textio.ads, libgnat/a-tideio.ads,
	libgnat/a-tienio.ads, libgnat/a-tifiio.ads,
	libgnat/a-tiflio.ads, libgnat/a-tiinio.ads,
	libgnat/a-timoio.ads, libgnat/i-c.ads, libgnat/interfac.ads,
	libgnat/interfac__2020.ads, libgnat/s-atacco.ads,
	libgnat/s-stoele.ads: Annotate packages and subprograms with
	returning annotations.