Add the 6th argument to .ACCESS_WITH_SIZE

Add the 6th argument to .ACCESS_WITH_SIZE

to carry the TYPE of the flexible array.

Such information is needed during tree-object-size.cc.

We cannot use the result type or the type of the 1st argument
of the routine .ACCESS_WITH_SIZE to decide the element type
of the original array due to possible type casting in the
source code.

gcc/c/ChangeLog:

	* c-typeck.cc (build_access_with_size_for_counted_by): Add the 6th
	argument to .ACCESS_WITH_SIZE.

gcc/ChangeLog:

	* tree-object-size.cc (access_with_size_object_size): Use the type
	of the 6th argument for the type of the element.
	* internal-fn.cc (expand_ACCESS_WITH_SIZE): Update the comment with
	the 6th argument.

gcc/testsuite/ChangeLog:

	* gcc.dg/flex-array-counted-by-6.c: New test.