Only compile boost threads when threads are actually required.

git-svn-id: https://svn.dealii.org/trunk@18226 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/base/source/boost_threads.cc b/deal.II/base/source/boost_threads.cc
index 82e6ece2ee4e6a472b1a6450067c039d035cd228..4dfd65b9a894d1d22bd171dde684713be0c694c6 100644 (file)
--- a/deal.II/base/source/boost_threads.cc
+++ b/deal.II/base/source/boost_threads.cc
@@ -13,7 +13,7 @@
 
 #include <base/config.h>
 
-#ifndef DEAL_II_CAN_USE_CXX0X
+#if (DEAL_II_USE_MT == 1) && !defined(DEAL_II_CAN_USE_CXX0X)
 
 // of the C++ compiler doesn't completely support the C++0x standard (and
 // consequently we can't use std::thread, std::mutex, etc), then include all