Fix broken macOS LLDB build from r279314

[tfiala]

Summary

This change replaces angle brackets with quotes for a non-system header that is being included like a system one. The existing behavior breaks the LLDB Xcode build.

I think build break fixes are eligible for post-commit review, but since I hardly touch LLVM, I'm preferring to be safe rather than sorry.

(Also adding Adrian Prantl in case he gets to it sooner.)

[tfiala]

Committed after email with Duncan:
r279390

[tfiala]

Accepting so this can be closed.

[tfiala]

Closing - this was submitted a few weeks ago.

include/llvm/ADT/ilist_node.h

 // This file defines the ilist_node class template, which is a convenient
 // base class for creating classes that can be used with ilists.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_ILIST_NODE_H
 #define LLVM_ADT_ILIST_NODE_H
 
-#include <llvm/ADT/PointerIntPair.h>
+#include "llvm/ADT/PointerIntPair.h"
 
 namespace llvm {
 
 template<typename NodeTy>
 struct ilist_traits;
 template <typename NodeTy> struct ilist_embedded_sentinel_traits;
 template <typename NodeTy> struct ilist_half_embedded_sentinel_traits;