[libc++] Support different libc++ namespaces in the iterator test

libc++ allows changing the namespace, don't assume __1 in the test
to avoid the test failure if different namespace is being used.

Differential Revision: https://reviews.llvm.org/D56698

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@351220 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed