Make the code base clean under -Wwrite-strings.

I've also added that warning option and -Werror to the build script,
so that I'll find out if I break this property in future.

1 files changed, 1 insertions, 1 deletions

diff --git a/puzzles.h b/puzzles.h
index 11542a5..40f5bcb 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -325,7 +325,7 @@ void midend_supersede_game_desc(midend *me, const char *desc,
                                 const char *privdesc);
 char *midend_rewrite_statusbar(midend *me, const char *text);
 void midend_serialise(midend *me,
-                      void (*write)(void *ctx, void *buf, int len),
+                      void (*write)(void *ctx, const void *buf, int len),
                       void *wctx);
 const char *midend_deserialise(midend *me,
                                int (*read)(void *ctx, void *buf, int len),