Revert "rustc: propagate libiconv on darwin"

This reverts commit b6fc00b8f4.

Rust 1.66.0 contains a fix for libiconv being linked unconditionally on macOS, but this only applies to packages that don't depend on older versions of `libc`.

For now, let's go back to including libiconv in `buildInputs` by default for packages that use `buildRustPackage`. As packages bump their `libc` versions, we can eventually stop including it by default, and manually add it where needed.

pkgs/build-support/rust/build-rust-package/default.nix

@@ -134,6 +134,7 @@ stdenv.mkDerivation ((removeAttrs args [ "depsExtraArgs" "cargoUpdateHook" "carg
   ];
 
   buildInputs = buildInputs
+    ++ lib.optionals stdenv.hostPlatform.isDarwin [ libiconv ]
     ++ lib.optionals stdenv.hostPlatform.isMinGW [ windows.pthreads ];
 
   patches = cargoPatches ++ patches;

pkgs/development/compilers/rust/cargo.nix

@@ -1,7 +1,7 @@
 { lib, stdenv, pkgsHostHost
 , file, curl, pkg-config, python3, openssl, cmake, zlib
 , installShellFiles, makeWrapper, cacert, rustPlatform, rustc
-, libiconv, CoreFoundation, Security
+, CoreFoundation, Security
 , auditable ? false # TODO: change to true when this is the default
 }:
 
@@ -28,7 +28,7 @@ rustPlatform.buildRustPackage {
     (lib.getDev pkgsHostHost.curl)
   ];
   buildInputs = [ cacert file curl python3 openssl zlib ]
-    ++ lib.optionals stdenv.isDarwin [ libiconv CoreFoundation Security ];
+    ++ lib.optionals stdenv.isDarwin [ CoreFoundation Security ];
 
   # cargo uses git-rs which is made for a version of libgit2 from recent master that
   # is not compatible with the current version in nixpkgs.

pkgs/development/compilers/rust/rustc.nix

@@ -163,11 +163,9 @@ in stdenv.mkDerivation rec {
   ];
 
   buildInputs = [ openssl ]
-    ++ optionals stdenv.isDarwin [ Security ]
+    ++ optionals stdenv.isDarwin [ libiconv Security ]
     ++ optional (!withBundledLLVM) llvmShared;
 
-  depsTargetTargetPropagated = optionals stdenv.isDarwin [ libiconv ];
-
   outputs = [ "out" "man" "doc" ];
   setOutputFlags = false;