diagnostic: rename new permerror overloads

While checking another change, I noticed that the new permerror overloads
break gettext with "permerror used incompatibly as both
 --keyword=permerror:2 --flag=permerror:2:gcc-internal-format and
 --keyword=permerror:3 --flag=permerror:3:gcc-internal-format".  So let's
change the name.

gcc/ChangeLog:

	* diagnostic-core.h (permerror): Rename new overloads...
	(permerror_opt): To this.
	* diagnostic.cc: Likewise.

gcc/cp/ChangeLog:

	* typeck2.cc (check_narrowing): Adjust.