Fix build with -Werror=format-security.

diff -upr vorbisgain-0.37.orig/misc.c vorbisgain-0.37/misc.c
--- vorbisgain-0.37.orig/misc.c	2023-04-23 10:28:06.652719371 +0200
+++ vorbisgain-0.37/misc.c	2023-04-23 10:28:27.952745282 +0200
@@ -56,7 +56,7 @@ void file_error(const char* message, ...
     vfprintf(stderr, message, args);
     va_end(args);
 
-    fprintf(stderr, strerror(err_num));
+    fputs(strerror(err_num), stderr);
     fprintf(stderr, "\n");
 }
 
