All non-x86 architectures need -pthread to link with threads enabled.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -135,7 +135,7 @@ ENDIF(WIN32)
 
 ADD_EXECUTABLE(pgagent ${_srcs})
 TARGET_LINK_LIBRARIES(
-        pgagent ${PG_LIBRARIES} ${Boost_LIBRARIES}
+        pgagent ${PG_LIBRARIES} ${Boost_LIBRARIES} -pthread
 )
 
 # Installation
