Move IdDeclInfoMap class in an anonymous namespace. Suggestion by Chris Lattner.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@49628 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/IdentifierResolver.h b/lib/Sema/IdentifierResolver.h
index abe568d..34b4764 100644
--- a/lib/Sema/IdentifierResolver.h
+++ b/lib/Sema/IdentifierResolver.h
@@ -43,8 +43,9 @@
   NamedDecl *Lookup(const IdentifierInfo *II, unsigned NSI);
 
 private:
-  class IdDeclInfoMap;
-  IdDeclInfoMap &IdDeclInfos;
+  // An instance of IdDeclInfoMap class, that's hidden away in the
+  // implementation file.
+  void *IdDeclInfos;
 };
 
 } // end namespace clang