gdb: Fix use after free bug in compile_object_run

gdb: Fix use after free bug in compile_object_run

In this commit:

  commit 6108fd1823f9cf036bbbe528ffcdf2fee489b40a
  Date:   Thu Sep 17 11:47:50 2020 -0600

      Use htab_up in type copying

A use after free bug was introduced.  In compile-object-run.c, in the
function compile_object_run, the code used to look like this:

    htab_t copied_types;

    /* .... snip .... */

    /* OBJFILE may disappear while FUNC_TYPE still will be in use.  */
    copied_types = create_copied_types_hash (objfile);
    func_type = copy_type_recursive (objfile, func_type, copied_types);
    htab_delete (copied_types);

    /* .... snip .... */

    call_function_by_hand_dummy (func_val, NULL, args,
                                 do_module_cleanup, data);

The copied_types table exists on the obstack of objfile, but is
deleted once the call to copy_type_recursive has been completed.

After the change the code now looks like this:

    /* OBJFILE may disappear while FUNC_TYPE still will be in use.  */
    htab_up copied_types = create_copied_types_hash (objfile);
    func_type = copy_type_recursive (objfile, func_type, copied_types.get ());

    /* .... snip .... */

    call_function_by_hand_dummy (func_val, NULL, args,
                                 do_module_cleanup, data);

The copied_types is now a unique_ptr and deleted automatically when it
goes out of scope.

The problem however is that objfile, and its included obstack, may be
deleted by the call to do_module_cleanup, which is called by
call_function_by_hand_dummy.

This means that in the new code the objfile, and its obstack, are
deleted before copied_types is deleted, and as copied_types is on the
objfiles obstack, we are now reading undefined memory.

The solution in this commit is to wrap the call to
create_copied_types_hash and copy_type_recursive into a new static
helper function.  The htab_up will then be deleted within the new
function's scope, before objfile is deleted.

This resolves some non-deterministic test failures I was seeing in
gdb.compile/*.exp tests.

gdb/ChangeLog:

	* compile/compile-object-run.c (create_copied_type_recursive): New
	function.
	(compile_object_run): Use new function.