We don't need to do the fancy dance with checking whether the iterator
represents a #define -- in fact, that's the wrong thing to do. The thing to do
is check whether the highest-priority module that did something to the module
#defined or #undefd it. If it #defined it, then the MacroInfo* will be non-NULL
and we're good to go.
llvm-svn: 241651
007135e612