nix: Go around a linker issue on Darwin (#58070)

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Release Notes:

- N/A

nix/build.nix

@@ -38,6 +38,7 @@
   libxfixes,
   libxkbcommon,
   libxrandr,
+  lld,
   libx11,
   libxcb,
   nodejs_22,
@@ -137,6 +138,8 @@ let
       ]
       ++ lib.optionals stdenv'.hostPlatform.isLinux [ makeWrapper ]
       ++ lib.optionals stdenv'.hostPlatform.isDarwin [
+        # Provides `ld64.lld` for clang's `-fuse-ld=lld`.
+        lld
         (cargo-bundle.overrideAttrs (
           new: old: {
             version = "0.6.1-zed";
@@ -246,6 +249,11 @@ let
         }";
 
         NIX_OUTPATH_USED_AS_RANDOM_SEED = "norebuilds";
+      }
+      // lib.optionalAttrs stdenv'.hostPlatform.isDarwin {
+        # Link with lld on Darwin. nixpkgs' classic open-source ld64 fails to insert
+        # ARM64 branch thunks for this binary, producing `b(l) ARM64 branch out of range`.
+        NIX_CFLAGS_LINK = "-fuse-ld=lld";
       };
 
       # prevent nix from removing the "unused" wayland/gpu-lib rpaths