clarified: proper trim_line for error;

--- a/src/Pure/Tools/ghc.ML	Sun Feb 21 11:53:05 2021 +0100
+++ b/src/Pure/Tools/ghc.ML	Sun Feb 21 12:24:40 2021 +0100
@@ -83,10 +83,10 @@
   let
     val template_path = dir + (Path.basic name |> Path.ext "hsfiles");
     val _ = File.write template_path (project_template {depends = depends, modules = modules});
-    val {rc, err, ...} =
-      Isabelle_System.bash_process
+    val _ =
+      Isabelle_System.bash_output_check
         ("cd " ^ File.bash_path dir ^ "; isabelle ghc_stack new " ^ Bash.string name ^
           " --bare " ^ File.bash_platform_path template_path);
-  in if rc = 0 then () else error err end;
+  in () end;
 
 end;