This DR was already resolved for GCC 7.1 by the implementation of DR
2192, but we didn't have an explicit test for the behaviour that 2735
guarantees.

	* doc/xml/manual/intro.xml: Document LWG 2735 status.
	* include/bits/std_abs.h: Add comment about LWG 2735.
	* testsuite/26_numerics/headers/cstdlib/dr2735.cc: New test.

From-SVN: r268867