Backport boost fix for threading detection in GCC 4.7

See http://svn.boost.org/svn/boost/trunk r76133 "Fix threading detection in
GCC-4.7 experimental."  Without it, BOOST_DISABLE_THREADS would be defined when
compiling with GCC 4.7, which in turn would cause
boost/smart_ptr/detail/sp_counted_base.hpp to include a single-thread--mode
boost/smart_ptr/detaul/sp_counted_base_nt.hpp which is not suitable in a
multi-threaded scenario.

Change-Id: Ia30a5c2c241e2e135858a5cab3dd855d05db50c8

boost/boost_1_44_0-gthreads.patch

+--- misc/boost_1_44_0/boost/config/stdlib/libstdcpp3.hpp	2010-06-11 13:16:34.000000000 +0200
++++ misc/build/boost_1_44_0/boost/config/stdlib/libstdcpp3.hpp	2012-07-13 10:31:58.330127342 +0200
+@@ -31,7 +31,8 @@
+ 
+ #ifdef __GLIBCXX__ // gcc 3.4 and greater:
+ #  if defined(_GLIBCXX_HAVE_GTHR_DEFAULT) \
+-        || defined(_GLIBCXX__PTHREADS)
++        || defined(_GLIBCXX__PTHREADS) \
++        || defined(_GLIBCXX_HAS_GTHREADS)
+       //
+       // If the std lib has thread support turned on, then turn it on in Boost
+       // as well.  We do this because some gcc-3.4 std lib headers define _REENTANT

boost/makefile.mk

@@ -80,6 +80,10 @@ PATCH_FILES += boost_1_44_0-gcc4.7.patch
 # Clang warnings:
 PATCH_FILES += boost_1_44_0-clang-warnings.patch
 
+# Backport http://svn.boost.org/svn/boost/trunk r76133 "Fix threading detection
+# in GCC-4.7 experimental":
+PATCH_FILES += boost_1_44_0-gthreads.patch
+
 ADDITIONAL_FILES= \
     libs/thread/src/win32/makefile.mk \
 	libs/date_time/src/gregorian/makefile.mk