Add basic support for the libc++ standard library

[SVN r68785]

include/boost/config/stdlib/libcpp.hpp

@@ -0,0 +1,22 @@
+//  (C) Copyright Christopher Jefferson 2011.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+//  See http://www.boost.org for most recent version.
+
+//  config for libc++
+//  Might need more in here later.
+
+#if !defined(_LIBCPP_VERSION)
+#  include <ciso646>
+#  if !defined(_LIBCPP_VERSION)
+#      error "This is not libc++!"
+#  endif
+#endif
+
+#define BOOST_STDLIB "libc++ version " BOOST_STRINGIZE(_LIBCPP_VERSION)
+
+#define BOOST_HAS_THREADS
+
+//  --- end ---