Need libs for Linux test build

test/CMakeLists.txt

@@ -9,6 +9,18 @@ ELSE ()
   SET(CERTDIR $ENV{TRAVIS_BUILD_DIR}/test/ssl)
 ENDIF ()
 
+IF (WIN32)
+    SET(LIBS_SYSTEM ws2_32)
+ELSEIF (UNIX)
+    IF(CMAKE_SYSTEM_NAME MATCHES "Linux")
+        SET(LIBS_SYSTEM c dl pthread)
+    ELSEIF (CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
+        SET(LIBS_SYSTEM compat pthread)
+    ELSE()
+        SET(LIBS_SYSTEM c pthread)
+    ENDIF()
+ENDIF()
+
 IF (PAHO_WITH_SSL)
     SET(OPENSSL_SEARCH_PATH "" CACHE PATH "Directory containing OpenSSL libraries and includes")