Fix a comment typo and add a couple suggestions from Chris.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@49066 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index e30f4b2..a91d3da 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -99,7 +99,8 @@
   /// with @compatibility_alias, so that we can emit errors on duplicates and
   /// find the declarations when needed. This construct is ancient and will
   /// likely never be seen. Nevertheless, it is here for compatibility.
-  typedef llvm::DenseMap<IdentifierInfo*, ObjCCompatibleAliasDecl*> ObjCAliasTy;
+  typedef llvm::DenseMap<const IdentifierInfo*, 
+                         ObjCCompatibleAliasDecl*> ObjCAliasTy;
   ObjCAliasTy ObjCAliasDecls;
   
   // Enum values used by KnownFunctionIDs (see below).