Revert "[Dwarf] Disable reference verification for now (PR32972)"

This reverts commit r302520 because it break the unit tests.

llvm-svn: 302524
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
index 024ddf5..8a54429 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
@@ -172,8 +172,7 @@
       }
     }
   }
-  // FIXME: This introduced unexplained failures on buildbots (PR32972)
-  //verifyDebugInfoReferences();
+  verifyDebugInfoReferences();
   return NumDebugInfoErrors == 0;
 }