treewide: replace stdenv.is with stdenv.hostPlatform.is

[Artturin]

Approve or thumbs up to show that you approve of the idea, or request changes on the first file to discuss why you don't think it's a good idea.

Join https://matrix.to/#/#stdenv:nixos.org to discuss

I'll reset to master and rerun the commands before merge.
Further replacements can be done in the PR where the warnings are added.
The commits can be added to .git-blame-ignore-revs in a separate PR

treewide: replace stdenv.is with stdenv.hostPlatform.is

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
#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  "buildStdenv.is" "buildStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd  "effectiveStdenv.is" "effectiveStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd  "originalStdenv.is" "originalStdenv.hostPlatform.is"

The rebuilds are due to src ./. or similar

https://gist.github.com/Artturin/4cc1e73fc612cb7a79459a9bb6bc27a3

[Artturin]

Undrafting to get reviews from probably all the codeowners in nixpkgs.

To keep the emails to a minimum either approve or thumbs up the PR if the idea is okay, or if it needs changes then let's discuss in https://matrix.to/#/#stdenv:nixos.org

[K900]

Idea is OK, list of merge conflicts is scary. Maybe do this stepwise?

[roberth]

Suggested change

	] ++ lib.optional pkgs.stdenv.hostPlatform.isLinux pkgs.inotify-tools;
	] ++ lib.optional pkgs.stdenv.buildPlatform.isLinux pkgs.inotify-tools;

This probably applies to most conditionals for any nativeBuildInputs.