add -pthread to CXX_FLAGS

CMakeLists.txt

@@ -16,7 +16,7 @@ option (OPENDHT_PYTHON "Build Python bindings" OFF)
 option (OPENDHT_TOOLS "Build DHT tools" ON)
 option (OPENDHT_DEBUG "Build with debug flags" OFF)
 
-set (CMAKE_CXX_FLAGS "-std=c++11 -Wno-return-type -Wall -Wextra -Wnon-virtual-dtor ${CMAKE_CXX_FLAGS}")
+set (CMAKE_CXX_FLAGS "-pthread -std=c++11 -Wno-return-type -Wall -Wextra -Wnon-virtual-dtor ${CMAKE_CXX_FLAGS}")
 
 find_package (GnuTLS 3.1 REQUIRED)
 find_package (Msgpack 1.1 REQUIRED)