Fix bug in strndup fix for windows. Move all includes out of headers and into code for strndup.h and move it to be the last include.

src/strndup.h

@@ -1,6 +1,11 @@
+#ifndef STRNDUP_H
+#define STRNDUP_H
+
+#include <config.h>
+
 #ifndef HAVE_STRNDUP
-#define HAVE_STRNDUP
 
 char *strndup(const char *s, size_t n);
 
-#endif /* HAVE_STRNDUP */
+#endif /* HAVE_STRNDUP */
+#endif /* STRNDUP_H */