Add libc++ and libc++abi to third-party.

third_party/libcxx/include/__undef_min_max

Index: third_party/libcxx/include/__undef_min_max
===================================================================
--- third_party/libcxx/include/__undef_min_max	(revision 0)
+++ third_party/libcxx/include/__undef_min_max	(revision 0)
@@ -0,0 +1,27 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef min
+#if defined(_MSC_VER) && ! defined(__clang__)
+_LIBCPP_WARNING("macro min is incompatible with C++.  #undefing min")
+#else
+#warning: macro min is incompatible with C++.  #undefing min
+#endif
+#undef min
+#endif
+
+#ifdef max
+#if defined(_MSC_VER) && ! defined(__clang__)
+_LIBCPP_WARNING("macro max is incompatible with C++.  #undefing max")
+#else
+#warning: macro max is incompatible with C++.  #undefing max
+#endif
+#undef max
+#endif