RPATH of libtcl and libtk shared objects is /tools/deps/lib

At the moment these shared libraries have an RPATH set to `/tools/deps/lib`:
```
$ objdump -x lib/libtcl8.6.so | grep RPATH
RPATH /tools/deps/lib
$ objdump -x lib/libtk8.6.so | grep RPATH
RPATH /tools/deps/lib:/tools/deps/lib
```

This doesn't seem correct, should we be avoiding adding an RPATH line or setting it relative to `$ORIGIN` or something?

I understand this has happened probably as a result of #676, but I'm not fully aware of the implications of this.

I can see that the Python binary has a `$ORIGIN` relative RPATH to load these shared libraries (which seems correct and intentional):
```
$ objdump -x bin/python3.13 | grep -i rpath
RPATH $ORIGIN/../lib