[Ada] Avoid uninitialized variable in bounded containers

[Ada] Avoid uninitialized variable in bounded containers

In function Copy in Ada.Containers.Bounded_Ordered_Sets and other
bounded containers packages, remove a possible use of an uninitialized
variable. This was not a bug, because the uninitialized variable could
be used only if checks are suppressed, and the checks would have failed,
leading to erroneous execution.

However, it seems more robust this way, and is probably equally
efficient, and avoids a warning that is given if checks are suppressed,
and the -Wall switch is given, and optimization is turned on.

2019-09-18  Bob Duff  <duff@adacore.com>

gcc/ada/

	* libgnat/a-cbhama.adb, libgnat/a-cbhase.adb,
	libgnat/a-cbmutr.adb, libgnat/a-cborma.adb,
	libgnat/a-cborse.adb, libgnat/a-cobove.adb (Copy): Avoid reading
	the uninitialized variable C in the Checks = False case. Change
	variable to be a constant.

gcc/testsuite/

	* gnat.dg/containers1.adb, gnat.dg/containers1.ads: New
	testcase.

From-SVN: r275839