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, 4 insertions, 3 deletions

diff --git a/signpost.c b/signpost.c
index 9c1c9ba..72f3ab2 100644
--- a/signpost.c
+++ b/signpost.c
@@ -497,10 +497,11 @@ static void free_game(game_state *state)
 }
 
 static void unpick_desc(const game_params *params, const char *desc,
-                        game_state **sout, char **mout)
+                        game_state **sout, const char **mout)
 {
     game_state *state = blank_game(params->w, params->h);
-    char *msg = NULL, c;
+    const char *msg = NULL;
+    char c;
     int num = 0, i = 0;
 
     while (*desc) {
@@ -845,7 +846,7 @@ generate:
 
 static const char *validate_desc(const game_params *params, const char *desc)
 {
-    char *ret = NULL;
+    const char *ret = NULL;
 
     unpick_desc(params, desc, NULL, &ret);
     return ret;