[Ada] Remove warnings-as-errors about constraints error in dead code

[Ada] Remove warnings-as-errors about constraints error in dead code

gcc/ada/

	* erroutc.ads, erroutc.adb (Is_Runtime_Raise): Global flag to
	connect status of initial messages and their continuation; we
	already have several flags like this.
	(Error_Msg_Object): Add field Warn_Runtime_Raise to connect
	error reporting (when problematic code is found) and removal
	(when problematic code is determined to be dead).
	* errout.adb (Error_Msg_Internal): Handle new field when
	recording a continuation message; propagate status from
	continuation to the preceding messages.
	(To_Be_Removed): For dead code remove both simple warnings and
	warnings about constraint errors that have been escalated to
	hard errors.
	(Set_Msg_Text): Recognize warnings about constraint errors that
	are escalated to hard errors.
	* errutil.adb (Error_Msg): Handle added field when recording a
	new message.