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

third_party/libcxx/include/cfloat

Index: third_party/libcxx/include/cfloat
===================================================================
--- third_party/libcxx/include/cfloat	(revision 0)
+++ third_party/libcxx/include/cfloat	(revision 0)
@@ -0,0 +1,78 @@
+// -*- C++ -*-
+//===--------------------------- cfloat -----------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_CFLOAT
+#define _LIBCPP_CFLOAT
+
+/*
+    cfloat synopsis
+
+Macros:
+
+    FLT_ROUNDS
+    FLT_EVAL_METHOD     // C99
+    FLT_RADIX
+
+    FLT_MANT_DIG
+    DBL_MANT_DIG
+    LDBL_MANT_DIG
+
+    DECIMAL_DIG         // C99
+
+    FLT_DIG
+    DBL_DIG
+    LDBL_DIG
+
+    FLT_MIN_EXP
+    DBL_MIN_EXP
+    LDBL_MIN_EXP
+
+    FLT_MIN_10_EXP
+    DBL_MIN_10_EXP
+    LDBL_MIN_10_EXP
+
+    FLT_MAX_EXP
+    DBL_MAX_EXP
+    LDBL_MAX_EXP
+
+    FLT_MAX_10_EXP
+    DBL_MAX_10_EXP
+    LDBL_MAX_10_EXP
+
+    FLT_MAX
+    DBL_MAX
+    LDBL_MAX
+
+    FLT_EPSILON
+    DBL_EPSILON
+    LDBL_EPSILON
+
+    FLT_MIN
+    DBL_MIN
+    LDBL_MIN
+
+*/
+
+#include <__config>
+#include <float.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+#ifndef FLT_EVAL_METHOD
+#define FLT_EVAL_METHOD __FLT_EVAL_METHOD__
+#endif
+
+#ifndef DECIMAL_DIG
+#define DECIMAL_DIG __DECIMAL_DIG__
+#endif
+
+#endif  // _LIBCPP_CFLOAT