[PATCH] Define std::sample for C++17

[Jonathan Wakely <jwakely at redhat dot com>]

I forgot that std::sample() was added to C++17, so it wasn't in our
status table. It is now.

I changed the testcase to use our iterator wrappers instead of
containers, which found some bugs. I intend to go through other tests
where I've used std::forward_list to get forward iterators, or stream
iterators for input/output iterators, and make them use the wrappers
too.

	* doc/xml/manual/status_cxx2017.xml: Add std::sample status.
	* doc/html/*: Regenerate.
	* include/experimental/algorithm (__sample): Move to bits/stl_algo.h
	and into namespace std.
	* include/bits/stl_algo.h (__sample): Define here. Fix invalid use
	of input iterator. Defend against overloaded comma operator.
	(sample): Define for C++17.
	* testsuite/25_algorithms/sample/1.cc: New test.

Tested powerpc64le-linux, committed to trunk.

Attachment: patch.txt
Description: Text document