Use a std::map so that we record the group ID.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174910 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Bitcode/Reader/BitcodeReader.h b/lib/Bitcode/Reader/BitcodeReader.h
index 8d36e67..28674eb 100644
--- a/lib/Bitcode/Reader/BitcodeReader.h
+++ b/lib/Bitcode/Reader/BitcodeReader.h
@@ -149,7 +149,7 @@
   std::vector<AttributeSet> MAttributes;
 
   /// \brief The set of attribute groups.
-  std::vector<AttributeSet> MAttributeGroups;
+  std::map<unsigned, AttributeSet> MAttributeGroups;
 
   /// FunctionBBs - While parsing a function body, this is a list of the basic
   /// blocks for the function.