<rdar://problem/16424592>

For some reason, the libc++ vector<bool> data formatter was essentially a costly no-up, doing everything required of it, except actually generating the child values!

This restores its functionality



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@205259 91177308-0d34-0410-b5e6-96231b3b80d8