Fix TestDataFormatterLibcxxListLoop.py test
Summary:
The compilation of the TestDataFormatterLibcxxListLoop.py currently fails with this error:
```
functionalities/data-formatter/data-formatter-stl/libcxx/list/loop/main.cpp:19:24: error: no member named '__value_' in 'std::__1::__list_node_base<int, void *>'
assert(third_elem->__value_ == 3);
~~~~~~~~~~ ^
```
It seems the internal structure of list has changed with the 3.8 release. This patch makes the test compile with the current libc++ and with the previous libc++.
Reviewers: shafik, zturner, labath
Reviewed By: labath
Subscribers: christof, jdoerfert, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D58273
llvm-svn: 354202