To keep this for the future we also strictDeps where possible, including for janePackages, topkg, oasis and ocamlbuild.
This makes some closures significantly smaller and makes cross compilation easier
9a778368f2 "move destdir creation to installPhase" moved directory
creation to preInstallHooks and exposed a bug in ocaml_libvirt:
```
ocaml-libvirt> ocamlfind install -ldconf ignore libvirt \
ocaml-libvirt> ../META *.so *.a *.cma *.cmx *.cmxa *.cmi *.mli
ocaml-libvirt> ocamlfind: Bad configuration: Cannot mkdir
/nix/store/...aml-libvirt-0.6.1.5/lib/ocaml/4.12.0/site-lib/libvirt
because a path component does not exist or is not a directory
ocaml-libvirt> make[1]: *** [Makefile:134: install-opt] Error 2
```
The change restore pre/post phases by overriding build targets instead
of overriding full phases.
