Include libgen.h in opt.c to fix win32 compilation warnings.
diff --git a/ccan/opt/opt.c b/ccan/opt/opt.c
index e3ccdbd..9bc34d9 100644
--- a/ccan/opt/opt.c
+++ b/ccan/opt/opt.c
@@ -7,6 +7,7 @@
#ifndef WIN32
#include <err.h>
#else
+#include <libgen.h>
#define errx(status, fmt, ...) { \
fprintf(stderr, fmt, __VA_ARGS__); \
fprintf(stderr, "\n"); \