[test] forwardlist.cons/move_noexcept.pass.cpp

* Don't forbid non-libc++ implementations from strengthening noexcept on forward_list's move constructor.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@314459 91177308-0d34-0410-b5e6-96231b3b80d8