gnutls: fix cross-compilation failure since 3.8.12 (#499659)

pkgs/by-name/gn/gnutls/package.nix

@@ -117,6 +117,13 @@ stdenv.mkDerivation rec {
   # https://gitlab.com/gnutls/gnutls/-/issues/1721
   + ''
     sed '2iexit 77' -i tests/system-override-compress-cert.sh
+  ''
+  # Upstream packaging bug: stamp_error_codes is missing from EXTRA_DIST in
+  # the release tarball, causing the build to try regenerating it by compiling
+  # and running `errcodes` — which fails when cross-compiling since the binary
+  # is for the target architecture. https://gitlab.com/gnutls/gnutls/-/issues/1797
+  + lib.optionalString (stdenv.buildPlatform != stdenv.hostPlatform) ''
+    touch doc/stamp_error_codes
   '';
 
   preConfigure = "patchShebangs .";