ada: Minor cleanups in generic formal matching

ada: Minor cleanups in generic formal matching

Minor rewording of a warning.
Disallow positional notation for <> (but disable this check),
and fix resulting errors.
Copy use clauses.

gcc/ada/

	* sem_ch12.adb (Check_Fixed_Point_Actual): Minor rewording; it seems
	more proper to say "operator" rather than "operation".
	(Matching_Actual): Give an error for <> in positional notation.
	This is a syntax error. Disable this for now.
	(Analyze_Associations): Copy the use clause in all cases.
	The "mustn't recopy" comment seems wrong, because New_Copy_Tree
	preserves Slocs.
	* libgnat/a-ticoau.ads: Fix violation of new postion-box error.
	* libgnat/a-wtcoau.ads: Likewise.
	* libgnat/a-ztcoau.ads: Likewise.