isabelle: mark cross compilation as broken

pkgs/by-name/is/isabelle/package.nix

@@ -330,7 +330,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   meta = {
     description = "Generic proof assistant";
-
     longDescription = ''
       Isabelle is a generic proof assistant.  It allows mathematical formulas
       to be expressed in a formal language and provides tools for proving those
@@ -346,6 +345,9 @@ stdenv.mkDerivation (finalAttrs: {
       lib.maintainers.jvanbruegge
       lib.maintainers.sempiternal-aurora
     ];
+    # need to compile the heaps for host on build
+    # which requires us to use the host polyml toolchain
+    broken = !(stdenv.buildPlatform.canExecute stdenv.hostPlatform);
     platforms = [
       "x86_64-linux"
       "aarch64-linux"