HDFFV-9984 add missing ref file

tools/test/h5repack/testfiles/h5copy_extlinks_src-base.h5copy_extlinks_src.h5.ddl

@@ -0,0 +1,28 @@
+HDF5 "out-h5copy_extlinks_src-mergeprune.h5copy_extlinks_src.h5" {
+GROUP "/" {
+   GROUP "group_ext" {
+      DATATYPE "extlink_datatype" H5T_STD_I32LE;
+      DATASET "extlink_dset" {
+         DATATYPE  H5T_STD_I32LE
+         DATASPACE  SIMPLE { ( 6 ) / ( 6 ) }
+         STORAGE_LAYOUT {
+            CONTIGUOUS
+            SIZE 24
+            OFFSET 2200
+         }
+         FILTERS {
+            NONE
+         }
+         FILLVALUE {
+            FILL_TIME H5D_FILL_TIME_IFSET
+            VALUE  H5D_FILL_VALUE_DEFAULT
+         }
+         ALLOCATION_TIME {
+            H5D_ALLOC_TIME_LATE
+         }
+      }
+      GROUP "extlink_grp" {
+      }
+   }
+}
+}