Introduce MetadataBase, a base class for MDString and MDNode.

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

llvm-svn: 76759

llvm/lib/Bitcode/Reader/BitcodeReader.h

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