Avoid Attr.h includes, CodeGen edition

This saves around 20 includes of Attr.h. Not much.
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index f9f25e7..c22504c 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -13,6 +13,7 @@
 #include "CGCXXABI.h"
 #include "CodeGenFunction.h"
 #include "CodeGenModule.h"
+#include "clang/AST/Attr.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/Basic/CodeGenOptions.h"