diff: fix leaking orderfile option

The `orderfile` diff option is being assigned via `OPT_FILENAME()`,
which assigns an allocated string to the variable. We never free it
though, causing a memory leak.

Change the type of the string to `char *` and free it to plug the leak.
This also requires us to use `xstrdup()` to assign the global config to
it in case it is set.

This leak is being hit in t7621, but plugging it alone does not make the
test suite pass.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/diff.h b/diff.h
index 9901c8ca8c..b95d3c1e83 100644
--- a/diff.h
+++ b/diff.h
@@ -235,7 +235,7 @@ enum diff_submodule_format {
  * diffcore library with.
  */
 struct diff_options {
-	const char *orderfile;
+	char *orderfile;
 
 	/*
 	 * "--rotate-to=<file>" would start showing at <file> and when