c++: Add tests for fixed PRs.

c++: Add tests for fixed PRs.

Bugzilla inspection turned up a bunch of old(er) PRs that have been
fixed.  Let's include them not to regress in the future.

gcc/testsuite/ChangeLog:

	PR c++/87530
	PR c++/58156
	PR c++/68828
	PR c++/86002
	PR c++/91525
	PR c++/96223
	PR c++/87032
	PR c++/35098
	* g++.dg/cpp0x/move-return4.C: New test.
	* g++.dg/cpp0x/vt-58156.C: New test.
	* g++.dg/cpp2a/concepts-pr68828.C: New test.
	* g++.dg/cpp2a/concepts-pr86002.C: New test.
	* g++.dg/cpp2a/concepts-pr91525.C: New test.
	* g++.dg/cpp2a/constexpr-indeterminate1.C: New test.
	* g++.dg/cpp2a/desig17.C: New test.
	* g++.dg/ext/attrib62.C: New test.