Add LINK_WITH_PTHREAD to CMakeList for explicitly adding pthread linking
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 4cbd162..2e202de 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -1,5 +1,6 @@
 option(USE_STATIC_POLARSSL_LIBRARY "Build PolarSSL static library." ON)
 option(USE_SHARED_POLARSSL_LIBRARY "Build PolarSSL shared library." OFF)
+option(LINK_WITH_PTHREAD "Explicitly link PolarSSL library to pthread." OFF)
 
 set(src
      aes.c
@@ -102,6 +103,9 @@
 		target_link_libraries(${polarssl_static_target} ${ZLIB_LIBRARIES})
 	endif(ZLIB_FOUND)
 
+	if(LINK_WITH_PTHREAD)
+        target_link_libraries(${polarssl_static_target} pthread)
+	endif()
 
 	install(TARGETS ${polarssl_static_target}
 			DESTINATION ${LIB_INSTALL_DIR}
@@ -118,6 +122,10 @@
 		target_link_libraries(polarssl ${ZLIB_LIBRARIES})
 	endif(ZLIB_FOUND)
 
+	if(LINK_WITH_PTHREAD)
+        target_link_libraries(polarssl pthread)
+	endif()
+
 	install(TARGETS polarssl
 			DESTINATION ${LIB_INSTALL_DIR}
 			PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE)