Don't build tests for Groonga

It fails on x86_64 OS X:

      CXXLD  test-dat.la
    Undefined symbols for architecture x86_64:
      "cut::inspect_c_string(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned int)", referenced from:
          void cut::assert_equal_reference<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, char const*, char const*) in test-dat.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    make[5]: *** [test-dat.la] Error 1

Reported by SHIMADA Koji. Thanks!!!