Make the AttrListPtr object a part of the LLVMContext.

When code deletes the context, the AttributeImpls that the AttrListPtr points to
are now invalid. Therefore, instead of keeping a separate managed static for the
AttrListPtrs that's reference counted, move it into the LLVMContext and delete
it when deleting the AttributeImpls.

llvm-svn: 168354
diff --git a/llvm/lib/VMCore/LLVMContextImpl.h b/llvm/lib/VMCore/LLVMContextImpl.h
index ee31814..90cf424 100644
--- a/llvm/lib/VMCore/LLVMContextImpl.h
+++ b/llvm/lib/VMCore/LLVMContextImpl.h
@@ -256,7 +256,8 @@
   FPMapTy FPConstants;
 
   FoldingSet<AttributesImpl> AttrsSet;
-  
+  FoldingSet<AttributeListImpl> AttrsLists;
+
   StringMap<Value*> MDStringCache;
 
   FoldingSet<MDNode> MDNodeSet;