Fix for threading support for Linux on arm.

[SVN r29964]

include/boost/config/stdlib/libstdcpp3.hpp

@@ -44,6 +44,12 @@
 #  define BOOST_DISABLE_THREADS
 #endif
 
+#if (defined(linux) || defined(__linux) || defined(__linux__)) && defined(__arm__) && defined(_GLIBCPP_HAVE_GTHR_DEFAULT)
+// linux on arm apparently doesn't define _REENTRANT 
+// so just turn on threading support whenever the std lib is thread safe:
+#  define BOOST_HAS_THREADS
+#endif
+
  
 #if !defined(_GLIBCPP_USE_LONG_LONG) \
     && !defined(_GLIBCXX_USE_LONG_LONG)\