spot: fix cross compilation

pkgs/by-name/sp/spot/package.nix

@@ -40,6 +40,12 @@ stdenv.mkDerivation rec {
     hash = "sha256-731aD+yJkyrNMmYtgKYzXIAyLegDBzTT2XqZs5usXiI=";
   };
 
+  postPatch = ''
+    substituteInPlace src/meson.build --replace-fail \
+      "cargo_output = 'src' / rust_target / meson.project_name()" \
+      "cargo_output = 'src' / '${stdenv.hostPlatform.rust.cargoShortTarget}' / rust_target / meson.project_name()"
+  '';
+
   nativeBuildInputs = [
     appstream-glib
     blueprint-compiler
@@ -71,6 +77,9 @@ stdenv.mkDerivation rec {
   # https://github.com/xou816/spot/issues/313
   mesonBuildType = "release";
 
+  # For https://github.com/xou816/spot/blob/21ee601f655caa4ca9cae1033a27459fe6289318/src/meson.build#L122
+  env.CARGO_BUILD_TARGET = stdenv.hostPlatform.rust.rustcTargetSpec;
+
   passthru = {
     updateScript = nix-update-script { };
   };