Also support the multilib (lib64) output directory

[chris-allan]

Artifacts from the native build may end up in a multilib output directory location:

callan@behemoth:~/code/TileDB-Java$ find build -name '*.so'
build/ep_tiledb-prefix/src/ep_tiledb-build/externals/src/ep_zlib-build/libz.so
build/ep_tiledb-prefix/src/ep_tiledb-build/externals/src/ep_zstd-build/lib/libzstd.so
build/ep_tiledb-prefix/src/ep_tiledb-build/externals/install/lib/libz.so
build/ep_tiledb-prefix/src/ep_tiledb-build/externals/install/lib64/libzstd.so
build/ep_tiledb-prefix/src/ep_tiledb-build/tiledb/tiledb/libtiledb.so
build/tiledb_jni/libtiledbjni.so
build/install/lib64/libtiledb.so

Also need to support that or certain dynamic libraries will not end up in the resulting JAR.