BUILD: Simplify build of simple_access_tests
Link test with existing libraries instead of building all
necessary source file on more time.
It's not portable to link with libsss_simple.so because it is a dynamic module
and not dynamic library.
*** Warning: Linking the executable simple_access-tests against the loadable module
*** libsss_simple.so is not portable!
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>