[Ada] New warning on not fully initialized box aggregate

[Ada] New warning on not fully initialized box aggregate

gcc/ada/

	* sem_aggr.adb (Resolve_Aggregate): Warn on not fully
	initialized box aggregate.
	* sem_aggr.ads: Fix typo.
	* sem_res.adb (Resolve_Actuals): Fix typo in error message
	format marking it incorrectly as a continuation message.
	* sem_elab.adb (Check_Internal_Call_Continue): Similarly, add
	missing primary message in case of a call to an actual generic
	subprogram.
	* sem_warn.adb (Check_References): Do not warn on read but never
	assigned variables if the type is partially initialized.
	* libgnat/a-except.ads, libgnat/a-ststun.ads,
	libgnat/g-sechas.ads, libgnat/a-cbdlli.ads,
	libgnat/a-cfdlli.ads, libgnat/a-cobove.ads,
	libgnat/a-cohata.ads, libgnat/a-crbltr.ads,
	libgnat/a-cbmutr.ads, libgnat/a-crdlli.ads,
	libgnat/a-cbsyqu.ads: Address new warning.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Update doc on -gnatwv.
	* gnat_ugn.texi: Regenerate.

gcc/testsuite/

	* gnat.dg/opt11.adb: Add new expected warning.