cmake: don't link APPLE with SYSTEM

Change-Id: I2e790f2f4c6240cd81258258c0df72ae278d372f
diff --git a/CMakeLists.txt b/CMakeLists.txt
index af085df..a458489 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -73,7 +73,7 @@
 add_library(dhtnet ${dhtnet_SOURCES})
 target_link_libraries(dhtnet PUBLIC PkgConfig::opendht PkgConfig::pjproject fmt::fmt ${MSGPACK_LIB})
 if (APPLE)
-    target_link_libraries(dhtnet PRIVATE SYSTEM "-framework CoreFoundation" "-framework Security" "resolv")
+    target_link_libraries(dhtnet PRIVATE "-framework CoreFoundation" "-framework Security" "resolv")
 endif()
 
 target_include_directories(dhtnet PUBLIC