In preparation for the deprecation of `stdenv.isX`.
These shorthands are not conducive to cross-compilation because they
hide the platforms.
Darwin might get cross-compilation for which the continued usage of `stdenv.isDarwin` will get in the way
One example of why this is bad and especially affects compiler packages
https://www.github.com/NixOS/nixpkgs/pull/343059
There are too many files to go through manually but a treewide should
get users thinking when they see a `hostPlatform.isX` in a place where it
doesn't make sense.
```
fd --type f "\.nix" | xargs sd --fixed-strings "stdenv.is" "stdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "stdenv'.is" "stdenv'.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "clangStdenv.is" "clangStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "gccStdenv.is" "gccStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "stdenvNoCC.is" "stdenvNoCC.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "inherit (stdenv) is" "inherit (stdenv.hostPlatform) is"
fd --type f "\.nix" | xargs sd --fixed-strings "buildStdenv.is" "buildStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "effectiveStdenv.is" "effectiveStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "originalStdenv.is" "originalStdenv.hostPlatform.is"
```
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.
