CMake: (fix) Threads dependency

- If the HDF5 library has been build with either thread-safety or
  subfiling VFD feature on it will have an additional dependency
  on a threading library. This dependency has been added to the
  hdf-config.cmake.in file.

config/cmake/hdf5-config.cmake.in

@@ -69,6 +69,11 @@ if (${HDF5_PACKAGE_NAME}_ENABLE_PARALLEL)
   find_package(MPI QUIET REQUIRED)
 endif ()
 
+if (${HDF5_PACKAGE_NAME}_ENABLE_THREADSAFE OR ${HDF5_PACKAGE_NAME}_ENABLE_SUBFILING_VFD)
+  set(THREADS_PREFER_PTHREAD_FLAG ON)
+  find_package(Threads QUIET REQUIRED)
+endif ()
+
 if (${HDF5_PACKAGE_NAME}_BUILD_JAVA)
   set (${HDF5_PACKAGE_NAME}_JAVA_INCLUDE_DIRS
       @PACKAGE_CURRENT_BUILD_DIR@/lib/jarhdf5-@HDF5_VERSION_STRING@.jar