iOS: Remove clang-wrapper?

[whs]

I'm not sure if I managed to find the correct root cause.

On macOS, building for iOS it is pretty much required to use the cross compiler.

When using pkgs.rust-bin.selectLatestNightlyWith, it propagate the clang-wrapper build input. Nix's clang-wrapper do not support cross building, and so it is not possible to build iOS applications.

Error message:

  cargo:warning=Warning: supplying the --target aarch64-apple-ios != arm64-apple-darwin argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead.

[simonzkl]

There was an attempt to override the stdenv in #216

Though personally I wish we would not propagate the stdenv in the first place, so I could put whatever I like there.