Avoid expecting nonzero size for access none void* arguments [PR101751].

Avoid expecting nonzero size for access none void* arguments [PR101751].

Resolves:
PR middle-end/101751 - attribute access none with void pointer expects nonzero size

gcc/ChangeLog:

	PR middle-end/101751
	* doc/extend.texi (attribute access): Adjust.
	* gimple-ssa-warn-access.cc (pass_waccess::maybe_check_access_sizes):
	Treat access mode none on a void* argument as expecting as few as
	zero bytes.

gcc/testsuite/ChangeLog:

	PR middle-end/101751
	* gcc.dg/Wstringop-overflow-86.c: New test.