message: Make unavailable functions FATAL.
diff: @@ -31,7 +31,7 @@ limitations under the License.
  Struct->FnName##Fn = \
  reinterpret_cast<decltype(FnName)*>(dlsym(library_handle, #FnName)); \
  if (!(Struct->FnName##Fn)) { \
  - LOG(ERROR) << #FnName " not available in this library."; \
  + LOG(FATAL) << #FnName " not available in this library."; \
  return errors::Unimplemented(#FnName " not available in this library."); \
  }
  