diff: make diff_set_default_prefix() static

This is not something an external caller would want to call; it
instead is an implementation detail of finalizing the effect other
functions (like diff_set_mnemonic_prefix()) prepared into a
diff_options structure to be used.  Make it file-scope static to
avoid exposing it to the outside world.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

diff.c

@@ -3444,7 +3444,7 @@ void diff_set_noprefix(struct diff_options *options)
 	options->a_prefix = options->b_prefix = "";
 }
 
-void diff_set_default_prefix(struct diff_options *options)
+static void diff_set_default_prefix(struct diff_options *options)
 {
 	options->a_prefix = diff_src_prefix ? diff_src_prefix : "a/";
 	options->b_prefix = diff_dst_prefix ? diff_dst_prefix : "b/";

diff.h

@@ -498,7 +498,6 @@ void diff_tree_combined_merge(const struct commit *commit, struct rev_info *rev)
 
 void diff_set_mnemonic_prefix(struct diff_options *options, const char *a, const char *b);
 void diff_set_noprefix(struct diff_options *options);
-void diff_set_default_prefix(struct diff_options *options);
 
 int diff_can_quit_early(struct diff_options *);