Introduce MetadataBase, a base class for MDString and MDNode.

Derive MDString directly from MetadataBase. 
Introduce new bitcode block to hold metadata.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76759 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/BitcodeReader.h

@@ -210,6 +210,7 @@ private:
   bool RememberAndSkipFunctionBody();
   bool ParseFunctionBody(Function *F);
   bool ResolveGlobalAndAliasInits();
+  bool ParseMetadata();
 };
   
 } // End llvm namespace