nix: restore atf cross overlay dropped in #3810

nix/lib/patches.nix

@@ -8,6 +8,56 @@
       };
     }
   )
+  # atf 0.23's configure.ac uses AC_RUN_IFELSE for three probes that
+  # cannot execute a compiled test binary during cross-compilation,
+  # aborting with:
+  #   "configure: error: cannot run test program while cross compiling"
+  #
+  # This breaks the aarch64-apple-darwin cross-build chain:
+  #   atf → libiconv → apple-sdk-14.4 → bindings-node-js-napi-*
+  # See https://github.com/xmtp/libxmtp/issues/3470
+  # and https://github.com/xmtp/libxmtp/issues/3476.
+  #
+  # Upstreamed as https://github.com/NixOS/nixpkgs/pull/510292 (merged,
+  # present in the current pin) — but the upstream seeds are gated on
+  # `!buildPlatform.canExecute hostPlatform`, and our nightly cross is
+  # aarch64-darwin → aarch64-apple-darwin: same arch and kernel, so
+  # canExecute is TRUE and the seeds never apply, while autoconf still
+  # decides cross_compiling=yes from the triple mismatch and aborts
+  # (broke the 2026-07-03 nightly after #3810 dropped this overlay).
+  # Keep this structurally-gated copy until the upstream gate is
+  # `buildPlatform != hostPlatform`; double-applying the seeds when
+  # both gates fire is harmless (same cache values).
+  #
+  # The three AC_RUN_IFELSE cache variables and their justifications:
+  #
+  #   kyua_cv_getopt_plus (m4/module-application.m4)
+  #     Tests whether getopt(3) accepts a leading '+' for POSIX
+  #     behavior. All target platforms (Darwin, glibc, musl) honour '+'.
+  #
+  #   kyua_cv_attribute_noreturn (m4/module-defs.m4)
+  #     Tests whether __attribute__((__noreturn__)) is supported by
+  #     checking GCC version >= 2.5. All modern GCC/Clang satisfy this.
+  #
+  #   kyua_cv_getcwd_works (m4/module-fs.m4)
+  #     Tests whether getcwd(NULL, 0) dynamically allocates. Both
+  #     Darwin and Linux (glibc and musl) support this.
+  #
+  # Pre-seeding all three is safe for every target in this flake.
+  # Gated on cross-compilation so native builds keep pulling from
+  # cache.nixos.org unchanged.
+  (
+    final: prev:
+    prev.lib.optionalAttrs (prev.stdenv.buildPlatform != prev.stdenv.hostPlatform) {
+      atf = prev.atf.overrideAttrs (old: {
+        configureFlags = (old.configureFlags or [ ]) ++ [
+          "kyua_cv_getopt_plus=yes"
+          "kyua_cv_attribute_noreturn=yes"
+          "kyua_cv_getcwd_works=yes"
+        ];
+      });
+    }
+  )
   # tcl 8.6.16 (pinned via nixpkgs 09061f74...) has multiple
   # cross-compile bugs when targeting *-unknown-linux-musl, and the
   # Hydra build farm only caches the x86_64-linux build host (not