PR #350299 broke Flutter's update script with how it handled getting the
platform. Furthermore, the problem was made worse in the last update to
Flutter which had to work around that problem. We'll just revert it for
now and do a proper fix once we can figure out how to satify setting the
different platforms without causing any more problems.
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"
```
Without this patch, `xcode_backend.sh` gets confused by the flutter SDK
`symlinkJoin` and picks up the `dart` executable from `flutter-unwrapped`,
which manifests in the following error during an iOS/macOS build:
```
Error (Xcode): Target debug_unpack_ios failed: Error: Flutter failed to create a directory at "/<nix-store-path>-flutter-3.24.1-unwrapped/bin/cache/artifacts".
```
Rationale:
With the advent of RFC 140, Nixpkgs becomes to promote self-contained package
directories and strongly discourages scattering along the old and deprecated
filesystem hierarchy.
Further, `build-support/flutter/*` is not referenced by any other expressions in
Nixpkgs besides flutter itself.
Further, concentrating all Flutter-related toolset below a same directory
hierarchy (arguably?) eases maintenance and future migrations.
