Improve warning locations (PR66208)

Improve warning locations (PR66208)

	PR c/66208
	* c-common.c (check_function_nonnull): Remove unnecessary declaration.
	Add new arg loc and pass it down as context.
	(check_nonnull_arg): Don't mark ctx arg as unused. Use it as a pointer
	to the location to use for the warning.
	(check_function_arguments): New arg loc.  All callers changed.  Pass
	it to check_function_nonnull.
	* c-common.h (check_function_arguments): Adjust declaration.

testsuite/
	PR c/66208
	* c-c++-common/pr66208.c: New file.

From-SVN: r232345