python310Packages.gssapi: support cross compilation

`GSSAPI_SUPPORT_DETECT` defaults to true and instructs setup.py to
perform a sanity check before enabling each gss extension. that sanity
check is to `dlopen` the dependency, which fails for cross compilation.

setting `GSSAPI_SUPPORT_DETECT=false` enables all extensions, it simply
bypasses the `dlopen` check.

pkgs/development/python-modules/gssapi/default.nix

@@ -33,6 +33,10 @@ buildPythonPackage rec {
       --replace 'get_output(f"{kc} gssapi --prefix")' '"${lib.getDev krb5}"'
   '';
 
+  env = lib.optionalAttrs (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) {
+    GSSAPI_SUPPORT_DETECT = "false";
+  };
+
   nativeBuildInputs = [
     cython
     krb5