Add dropped ManualDWARFIndex assert()

D47253 dropped this assertion.

Differential Revision: https://reviews.llvm.org/D60254

llvm-svn: 357678

lldb/source/Plugins/SymbolFile/DWARF/ManualDWARFIndex.cpp

@@ -92,6 +92,9 @@ void ManualDWARFIndex::Index() {
 }
 
 void ManualDWARFIndex::IndexUnit(DWARFUnit &unit, IndexSet &set) {
+  assert(!unit.GetSymbolFileDWARF()->GetBaseCompileUnit() &&
+      "DWARFUnit associated with .dwo or .dwp should not be indexed directly");
+
   Log *log = LogChannelDWARF::GetLogIfAll(DWARF_LOG_LOOKUPS);
 
   if (log) {