Move std::begin(array) and std::end(array) out from under an #ifdef that was preventing people from building libc++ using gcc. This corrects a mistake that I introduced in r196058

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@197061 91177308-0d34-0410-b5e6-96231b3b80d8