Set -undefined dynamic_lookup when linking on Mac OS X.

This fixes #822.

cpp/CMakeLists.txt

@@ -126,6 +126,8 @@ find_required_program (JAVA java
 if (APPLE)
   FIND_LIBRARY (COREFOUNDATION_LIB CoreFoundation)
   FIND_LIBRARY (FOUNDATION_LIB Foundation)
+  set (CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS
+    "${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS} -undefined dynamic_lookup")
 endif ()
 
 if (${USE_STD_MAP} STREQUAL "OFF")