any_cast doesn't work with rvalue reference targets and cannot
move with a value target.
* include/experimental/any (any(_ValueType&&)): Constrain and
add an overload that doesn't forward.
(any_cast(any&&)): Constrain and add an overload that moves.
* testsuite/experimental/any/misc/any_cast.cc: Add tests for
the functionality added by LWG 2509.
From-SVN: r238022