This is essential for iterating across macros properly, which LLDB does when
loading macros from modules.  A naiver version of this patch (without the
conditional) caused assertion failures in the testsuite, but this version should
be safe.

Thanks to Ben Langmuir for the refinement that made this work.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@269554 91177308-0d34-0410-b5e6-96231b3b80d8