silence "no symbols" warnings on apple clang

fixes #1252
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 6177ca2..cd1857c 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -96,6 +96,13 @@
     set(libs ${libs} ws2_32)
 endif(WIN32)
 
+if(APPLE)
+    SET(CMAKE_C_ARCHIVE_CREATE   "<CMAKE_AR> Scr <TARGET> <LINK_FLAGS> <OBJECTS>")
+    SET(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> Scr <TARGET> <LINK_FLAGS> <OBJECTS>")
+    SET(CMAKE_C_ARCHIVE_FINISH   "<CMAKE_RANLIB> -no_warning_for_no_symbols -c <TARGET>")
+    SET(CMAKE_CXX_ARCHIVE_FINISH "<CMAKE_RANLIB> -no_warning_for_no_symbols -c <TARGET>")
+endif(APPLE)
+
 if(USE_PKCS11_HELPER_LIBRARY)
     set(libs ${libs} pkcs11-helper)
 endif(USE_PKCS11_HELPER_LIBRARY)