IR: Allow multiple global metadata attachments with the same type.

This will be necessary to allow the global merge pass to attach
multiple debug info metadata nodes to global variables once we reverse
the edge from DIGlobalVariable to GlobalVariable.

Differential Revision: http://reviews.llvm.org/D20414

llvm-svn: 271358

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -4167,7 +4167,7 @@ std::error_code BitcodeReader::parseGlobalObjectAttachment(
     MDNode *MD = MetadataList.getMDNodeFwdRefOrNull(Record[I + 1]);
     if (!MD)
       return error("Invalid metadata attachment");
-    GO.setMetadata(K->second, MD);
+    GO.addMetadata(K->second, *MD);
   }
   return std::error_code();
 }