darwin.Csu: drop

pkgs/by-name/ap/apple-sdk/common/propagate-inputs.nix

@@ -48,17 +48,13 @@ in
 self: super: {
   # These packages are propagated only because other platforms include them in their libc (or otherwise by default).
   # Reducing the number of special cases required to support Darwin makes supporting it easier for package authors.
-  propagatedBuildInputs =
-    super.propagatedBuildInputs or [ ]
-    ++ [
-      libiconv
-      darwin.libresolv
-      darwin.libsbuf
-      # Shipped with the SDK only as a library with no headers
-      (lib.getLib darwin.libutil)
-    ]
-    # x86_64-darwin links the object files from Csu when targeting very old releases
-    ++ lib.optionals stdenvNoCC.hostPlatform.isx86_64 [ darwin.Csu ];
+  propagatedBuildInputs = super.propagatedBuildInputs or [ ] ++ [
+    libiconv
+    darwin.libresolv
+    darwin.libsbuf
+    # Shipped with the SDK only as a library with no headers
+    (lib.getLib darwin.libutil)
+  ];
 
   # The Darwin module for Swift requires certain headers to be included in the SDK (and not just be propagated).
   buildPhase = super.buildPhase or "" + ''

pkgs/stdenv/darwin/default.nix

@@ -285,7 +285,6 @@ let
   };
   sdkDarwinPackages = prevStage: {
     inherit (prevStage.darwin)
-      Csu
       adv_cmds
       copyfile
       libiconv
@@ -1059,7 +1058,6 @@ assert bootstrapTools.passthru.isFromBootstrapFiles or false; # sanity check
             prevStage.updateAutotoolsGnuConfigScriptsHook
             prevStage.updateAutotoolsGnuConfigScriptsHook.gnu_config
           ]
-          ++ lib.optionals localSystem.isx86_64 [ prevStage.darwin.Csu ]
           ++ (with prevStage.darwin; [
             binutils
             binutils.bintools

pkgs/top-level/darwin-aliases.nix

@@ -108,6 +108,7 @@ stubs
 
   ### C ###
 
+  Csu = throw "darwin.Csu has been removed, as it was only used on `x86_64-darwin`, which is no longer supported"; # added 2026-06-26
   cctools = pkgs.cctools; # added 2024-07-17
   cctools-apple = pkgs.cctools; # added 2024-07-01
   cctools-llvm = pkgs.cctools; # added 2024-07-01