[Ada] Fix buffer overrun for small string concatenation at -O0

[Ada] Fix buffer overrun for small string concatenation at -O0

The concatenation routines may read too much data on the source side when
the destination buffer is larger than the final result.  This change makes
sure that this does not happen any more and also removes obsolete stuff.

gcc/ada/

	* rtsfind.ads (RE_Id): Remove RE_Str_Concat_Bounds_N values.
	(RE_Unit_Table): Remove RE_Str_Concat_Bounds_N entries.
	* libgnat/s-conca2.ads (Str_Concat_2): Adjust head comment.
	(Str_Concat_Bounds_2): Delete.
	* libgnat/s-conca2.adb (Str_Concat_2): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_2): Delete.
	* libgnat/s-conca3.ads (Str_Concat_3): Adjust head comment.
	(Str_Concat_Bounds_3): Delete.
	* libgnat/s-conca3.adb (Str_Concat_3): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_3): Delete.
	* libgnat/s-conca4.ads (Str_Concat_4): Adjust head comment.
	(Str_Concat_Bounds_4): Delete.
	* libgnat/s-conca4.adb (Str_Concat_4): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_4): Delete.
	* libgnat/s-conca5.ads (Str_Concat_5): Adjust head comment.
	(Str_Concat_Bounds_5): Delete.
	* libgnat/s-conca5.adb (Str_Concat_5): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_5): Delete.
	* libgnat/s-conca6.ads (Str_Concat_6): Adjust head comment.
	(Str_Concat_Bounds_6): Delete.
	* libgnat/s-conca6.adb (Str_Concat_6): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_6): Delete.
	* libgnat/s-conca7.ads (Str_Concat_7): Adjust head comment.
	(Str_Concat_Bounds_7): Delete.
	* libgnat/s-conca7.adb (Str_Concat_7): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_7): Delete.
	* libgnat/s-conca8.ads (Str_Concat_8): Adjust head comment.
	(Str_Concat_Bounds_8): Delete.
	* libgnat/s-conca8.adb (Str_Concat_8): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_8): Delete.
	* libgnat/s-conca9.ads (Str_Concat_9): Adjust head comment.
	(Str_Concat_Bounds_9): Delete.
	* libgnat/s-conca9.adb (Str_Concat_9): Use the length of the last
	input to size the last assignment.
	(Str_Concat_Bounds_9): Delete.