Fix TokuDB Not building

We don't check for DLSYM in CMake, check for DLOPEN instead.

storage/tokudb/CMakeLists.txt

 # ft-index only supports x86-64 and cmake-2.8.9+
 IF(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64" AND
-    NOT CMAKE_VERSION VERSION_LESS "2.8.9" AND HAVE_DLSYM)
+    NOT CMAKE_VERSION VERSION_LESS "2.8.9" AND HAVE_DLOPEN)
 CHECK_CXX_SOURCE_COMPILES(
 "
 struct a {int b; int c; };